Approving a government motion on the Withdrawal Agreement is just one of two steps needed for the UK to ratify the deal. The second is the passage of primary legislation to implement the Withdrawal Agreement, which must receive Royal Assent before the Brexit deadline of 29 March 2019. This note focuses on the political and procedural challenges to achieving that outcome, which are giving government whips increasing cause for concern.


Key points

  • The Withdrawal Bill will be substantial and controversial, ensuring the continued primacy of EU law and courts, potentially for an unspecified period, and legislating to provide for ongoing payments to the EU and potentially for a Northern Ireland specific backstop.


  • It is therefore likely to pit Brexiteers Conservative and Northern Irish Democratic Unionist MPs against the government, raising the prospect of amendments being passed by the UK Parliament that would undermine any agreement reached with the EU and pose a serious threat to ratification.


  • The pressure of time is now considerable. The six-month period for ratification originally envisaged by the government is likely to be squashed to three, making the Bill extremely vulnerable to delay and defeat.


  • The experience of parliamentary scrutiny of legislation to implement the Maastricht Treaty suggests there is a real risk that this bill could fail to beat the 29 March deadline.


  • The Maastricht legislation required 41 active parliamentary days, over a total period of over a year, during its passage through both Houses. it changed from being a one-page bill with two substantive clauses to being a two-page Act with seven substantive clauses


  • If the government manages to introduce a Withdrawal Bill after Christmas, an optimistic goal, it will only have 44 available parliamentary sitting days as things stand – and less than three months available in total time.


  • If the bill runs into trouble it will become very likely that the UK government will need to seek an extension of the Article 50 process, even if a deal is agreed before Christmas and a first parliamentary vote is won.

  1. The substance of a Withdrawal Agreement Bill

The government set out the broad content of the EU Withdrawal Agreement and Implementation Bill in a White Paper on implementation in July.[1] The bill will contain any necessary implementing provisions on the three key areas of the Withdrawal Agreement:

  1. the rights of EU citizens in the UK;
  2. the financial settlement the UK will make, including budget contributions during the transition period;
  3. the ‘backstop’ to prevent a hard border on the island of Ireland.

Each of these issues is still the subject of fierce debate in the UK. Even EU citizens’ rights are controversial in the context of the wider national debate about immigration and, in the adversarial media environment, as a potential bargaining counter with the EU27.

In addition, the bill will cover ‘safeguard’ measures for some of these Withdrawal Agreement rights in UK law. The UK has agreed the principle of extra constitutional locks over EU citizens’ rights but has not yet presented any details to parliament. In particular, the bill will need to cover:

  1. creating a constitutional “barrier” to a future UK parliament repealing the rights of EU citizens in the UK. Restrictions on parliamentary sovereignty are rare in UK law, and so likely to attract Parliamentary debate and potentially amendments;
  2. an independent monitoring mechanism for EU citizens’ rights, giving a new, UK body the same rights of investigation and initiating protective court proceedings as the European Commission currently has in the EU. This will create a ‘two tier’ set of legal protections, applying only to EU citizens in the UK;
  3. recognising certain EU-derived individual rights – such as recognition of professional qualifications – in UK law, for people who are already working in the UK. This could become linked to debates about reciprocity for UK citizens working in the EU;
  4. potentially extending restrictions on the effective return of powers from the EU to Scotland, Wales and Northern Ireland until the end of the transition period.

There is also a major requirement which cuts across most areas of UK law and policy: to suspend the effect of what was once known as ‘the Great Repeal Bill’ by continuing to make EU law supreme over UK law during the transition period.  The EU Withdrawal Act 2018 formally repeals the European Act Communities Act 1972, ending the jurisdiction of the European Court of Justice in the UK and the supremacy of EU law. This change, a totemic symbol of Brexit for many MPs, will be “saved” – that is, suspended – until the end of the transition period. UK law cannot be inconsistent with EU law during the transition.

The government plans to deal with other controversial areas, such as Fisheries policy, in separate legislation.

It is unlikely that the political declaration on the future EU-UK relationship will be covered in the bill. It is a political framework for the future talks, which will only start in earnest once the UK has left. The government will also be anxious to remove possible hooks for amendments pushing the UK towards a ‘Canada’-style Free Trade Agreement in future talks. But the framework for the future relationship which is sketched out in the declaration will be the ghost at the feast, providing the focus for Parliamentarians to continue a proxy war over rival visions of the UK’s future direction after leaving the EU.


  1. The focus of political division

The bill, then, will lay out with legal precision the immediate “vassal state” relationship which Brexiteer MPs have criticised. It will also make clear that, contrary to what many Brexiteer MPs have claimed, the financial settlement is not a payment for a future trade deal, but a separate settlement of accounts. This presents serious risks to ratification. For although parliament cannot change the Withdrawal Agreement, amendments which could in practice wreck the deal may be considered in the scope of the bill.

The Speaker may rule amendments out of scope if he has legal advice that such amendments would make it impossible for the UK to discharge its international treaty obligations. However, there could be ‘grey areas’ where the impact is not so clear-cut and which – if the amendment had widespread, especially cross-party support – the Speaker would find it hard to reject on principle.

To take three examples, the EU would probably have serious concerns about additional conditions imposed by parliament through the bill, such as:

  • making annual payments of the financial settlement subject to further parliamentary controls, or linked to Parliamentary approval of progress on the trade talks;
  • a parliamentary lock on new EU legislation during the transition. The government says that a lock would apply under its ‘Chequers’ plan for UK alignment with EU Single Market rules for goods in a future trade deal. We are likely to see the first attempts to create such a lock by amendment to the bill;
  • making implementation of essential elements of an Irish border ‘backstop’ subject to agreement by the Northern Ireland Executive and Assembly. These institutions are not sitting but, even when they are, either of the main parties in Northern Ireland effectively has a veto over major decisions. The EU would not accept amendments which gave the DUP an effective veto power over Northern Ireland following new EU rules, should the backstop ever be used.

Even where amendments might not wreck the Withdrawal Agreement, they could trigger fierce debate and delay ratification. We would expect, for example, to see amendments diluting the continued, automatic supremacy of EU law over UK law during the transition. Brexiteers will try to devise ways to give the UK Parliament an ultimate ‘constitutional’ lock over the ECJ – power which they have often claimed the German Constitutional Court holds. Amendments are also likely to seek to limit any extension of the transitional period.

On many of these issues the government is vulnerable because it has consistently accepted, at least implicitly, core Brexiteer arguments such as that the financial settlement is linked to the future trade deal terms, or that any transition will be short and explicitly time-limited.

We will also probably see attempts to limit the future scope of UK cooperation with the EU over trade or security. Parliament has already passed amendments to the Customs (Trade) Bill limiting the UK’s ability to follow the EU VAT regime, for example, and barring the UK from collecting customs duties on behalf of the EU.

Any such amendments which were passed in the House of Commons would almost certainly be rejected in the House of Lords, delaying the process further. This is the pattern we have seen over the key Brexit legislation so far; the original Withdrawal Bill was amended much more heavily by the Lords (15 times) than the government expected, and so took much longer to be passed by parliament.

From very different motives, there will also be attempts to pass an amendment requiring a new referendum before the UK could ratify the deal. Again, this is likely to take time, even assuming it is defeated.


  1. The collision of time and politics

The government has previously stated that the Withdrawal Agreement Bill will have a “normal passage” like any other piece of legislation. It will therefore go through all stages of the legislative process, though as a constitutional bill it will be heard on the floor of both Houses. If the vote on a Brexit deal comes on the eve of Christmas it is likely that the subsequent legislation will not be introduced until early January, with second reading likely the week of 7th January when the Commons returns from recess.

The bill must be passed and have received Royal Assent by 29 March in order for any Withdrawal Agreement to take effect. The government will table a programme motion with the aim of guaranteeing it beats that deadline. That is likely to meet some opposition, although it is unlikely that the House will deny the government’s ability to ratify an international treaty within the timescale required. Furthermore, although there are conventions about the passage of a bill, the government generally has significant control over the timing of parliamentary business in the Commons.  However that control is not guaranteed.

Given the time pressures at work, the bill is exposed to significant risks arising from any delay. The Institute for Government previously warned that if negotiations dragged on past October, or if parliament raised objections to a deal, then the original six-month timeframe for parliamentary ratification “could be unachievable”.[2] Negotiations now look certain to drag on past October, with December being talked about as a more likely ‘last-chance-saloon’ for a deal. That significantly narrows the window for parliamentary ratification to three months and means the process is highly vulnerable to political challenge. Given the controversy surrounding many of the bill’s key provisions the scope for guerrilla warfare from all sides is wide.

Parliamentary scrutiny of the legislation to implement the Maastricht Treaty illustrates the dangers that are likely to be presented. Like the proposed Withdrawal Bill it was designed to give domestic legal effect to an international treaty. As such it should have been well protected from amendments that could have been seen to breach the agreement on which it was based. Yet it changed from being a one-page bill with two substantive clauses to being a two-page Act with seven substantive clauses.[3] During its passage through the Commons the bill was subject to legal argument as to whether proposed amendments should be ruled out of order, with the Attorney General ultimately overruling argument from the Foreign Office. It is highly likely that the Withdrawal Agreement Bill would end up the subject of similar legal challenges about the legality of amendments.

The Maastricht Treaty should serve as a warning from history – recent history given that many of the leading protagonists are still MPs – about how government can lose control of events if parliament gets a grip. Significantly, in the context of the current situation, the Maastricht legislation was before parliament for 41 days. If the Commons were to follow the normal sitting pattern in the first quarter of next year, as the Chief Whip has said it will, then there look to be around 44 sitting days available to pass the Withdrawal Agreement Bill.

However, not all of that time would normally be available for government business. A certain amount of time is reserved in Standing Orders for backbench business and estimates days. Furthermore there are other things that the government may need to do; including, potentially, the Finance Bill. Although that is due to be introduced in early November the threat of wrecking amendments designed to block future EU payments may mean it is held back until after the motion to approve a deal.

It will therefore be an immense task of political management for government whips, who would have expended enormous political capital getting the deal initially approved, to beat the clock unscathed. This is before we consider the delaying potential of the House of Lords, which devoted enormous time to scrutinising and amending the Withdrawal Bill earlier this year.


  1. Conclusion

There is a serious risk that the government could lose votes on the bill that would have the effect of at least delaying it and, unless overturned, invalidating it against the agreement struck with Brussels.

If things start to go wrong during parliamentary scrutiny of the bill the government runs the risk of missing the deadline for ratifying the Withdrawal Agreement. In such circumstances it may become necessary to appeal for an extension of the Article 50 process – particularly given the knock-on effects that problems in UK ratification could have for the process in the European Parliament. Even if the EU 27 agreed to an extension, unanimously (as is required under Article 50), the practical limit is another six weeks. After that, the UK would need to field candidates for the European Parliament elections. All this underlines the enduring truth that the Brexit process will remain beset by uncertainty and risk until the very end – whenever that is.



  • Paul McGrade is senior counsel on Brexit at Lexington Communications. He is a former senior diplomat.
  • Declan McHugh is a director at Lexington Communications. He is a former special adviser to Jack Straw.

[1] DExEU, Legislating for the Withdrawal Agreement between the United Kingdom and the European Union

[2] Institute for Government, Voting on Brexit,

[3] House of Commons Library, Brexit: Parliament’s role in approving and implementing agreements with the European Union,