The PM’s announcement was totally at odds with all her previous statements, stretching back to the moment she became Conservative Party leader in July last year, in which she had steadfastly ruled out an early poll. That position was genuinely held.

But in recent weeks the Prime Minister and her closest advisers calculated that conditions had changed and that now was the moment to act on the political advantage she holds.

Fundamentally, they worried that the Government’s small Commons majority was insufficient to guarantee the passage of legislation required by Brexit, and could serve to undermine Britain’s position in negotiations with the EU.

A snap election is intended to strengthen the PM’s hand, increasing the Government’s majority by capitalising on the Conservative Party’s huge lead over Labour in the polls and pushing the date of the next election beyond 2020, easing pressure on issues like any transitional arrangements. The lack of activity in relation to the Brexit negotiations before the summer (due to the French elections) provides some cover over the timing.

Due to the Fixed Term Parliament’s Act the PM will need a two-thirds Commons majority to pass a motion to hold an early election. Despite the fact that many of her political opponents, notably Labour, have little to gain from an early poll, they will support it.

There is likely to be a short wash-up period over the next week or two in which legislation currently in train can be progressed quickly. The traditional election purdah period is likely to begin in late April. During this time government business will be pared back and ministerial meetings and visits become restricted. More generally, parliament will empty as MPs return to their constituencies to prepare for the poll.

The announcement of an early election looks likely to create more surprise than the result. A Times/YouGov poll published on Monday gave the Tories a 21-point lead over Labour – a nine-year high with the polling firm. The poll, which put the Tories’ support at 44%, versus Labour’s 23%, suggests Labour (currently with 230 MPs) could lose as many as 70 seats, handing the Tories a majority of between 100 and 150.

Even though the election will be fought on existing boundaries, Labour strategists cannot see any circumstance in which the party will not lose seats. The question is how badly Labour does. A long campaign is viewed as unfavourable, as it will expose the weakness of Jeremy Corbyn and the leadership team.

Meanwhile, many expect the Liberal Democrats to make a political recovery, perhaps increasing their vote share from 2015 by standing on an avowedly anti-Brexit agenda. In some areas, such as the South West, the Lib Dems may even be able to regain seats that they lost to the Tories. While they are less likely to take seats in the North, any increase in vote share would probably harm Labour, which gained from the Lib Dem collapse at the last election. The Conservatives clearly have their sights set on these Labour heartlands, which helps to explain the way Theresa May framed the forthcoming contest as the Brexit election.

The Prime Minister came to power through a Conservative leadership election in which all her main opponents disintegrated. She enters a general election facing the most ineffective opposition leader in living memory. If she can realise the advantage that the polls suggest, Theresa May will emerge from the contest with a stronger mandate and a more confident position in which to focus on the key challenge that still confronts her: negotiating Britain’s exit from the European Union.