Vox pops on television news may be unscientific but nonetheless display a consistent theme; former Labour voters are rejecting Jeremy Corbyn and prepared to switch directly to Theresa May. There is a growing sense that Britain is on the verge of what political scientists term a ‘critical election’ – an event that marks a dramatic and sudden political realignment giving rise to a new era of electoral dominance. In modern UK political history, such realignments may be seen to have taken place in 1979, when the Conservatives took power for 18 years, and 1997, after which New Labour dominated government for 13 years. 2017 is shaping up to be another such moment.

The local election baseline

If we are really are on the verge of a political earthquake then a significant tremor will likely be felt on 4 May, when local elections take place in all of Scotland and Wales, and in 34 predominantly ‘shire’ county council elections in England. In addition six ‘metro-mayor’ elections will take place in Greater Manchester, the West Midlands, Liverpool City Region, Peterborough and Cambridge, West of England and Tees Valley.

Most of these local elections were last fought in 2012 and 2013, when Labour performed strongly, as highlighted in the below infographic:

2012/2013 Local Election Results

Key local battlegrounds

The 2017 local elections are unusual for taking place in the midst of a general election campaign, and will be an important barometer of party strength in the run up to June 8th. While comparisons with overall vote shares from last time will provide some clues about the state of public support, contests in specific council areas will shine a light on the likely outcome of some key Westminster seats. Below we focus on seven significant battlegrounds:

Cardiff City Council
Labour holds over half the seats on the council and three out of the four Cardiff parliamentary seats (with the Conservatives holding Cardiff North). If polls pointing to an historic Tory breakthrough in Wales are to be realised then the Conservatives should improve their standing in the local elections here. Jeremy Corbyn held his first general election event in the city but Labour would do well to defend its position. It is under threat here not just from the Conservatives but from the Lib Dems, who are the second biggest group on the council and are targeting the Cardiff Central seat in June.

Nottinghamshire County Council
Nottinghamshire is a key battleground. Theresa May and Jeremy Corbyn launched their respective local election campaigns in the area earlier this month. If the Conservatives can win control from Labour it will point towards the loss of several long-held Labour parliamentary seats in the East Midlands. But if Labour can hang on it would suggest the party’s core support is holding up.

Lancashire County Council
The council has been Labour controlled for most of its history, but is currently closely balanced; Labour is currently the largest party with 39 councillors against 35 Tories, six Lib Dems, three independents and one Green. Lancashire is home to a number of marginal parliamentary seats and the local results will be an important indication about how those will play out in the June poll.

Somerset County Council
The county elections in Somerset, where the Lib Dems are seeking to overthrow the Conservatives, will be a key indicator as to whether a Liberal recovery will materialise in the West Country. UKIP took seats off the Tories in 2013 and the performance of that vote should be closely monitored.

Perth & Kinross Council
A key battleground in Scotland. The SNP won 18 of the 41 council seats in Perth and Kinross at the last local government elections in 2012, forming a minority administration, and hold the Westminster parliamentary seat with a majority of over 10,000. But the Scottish Tories have made this a key target and launched their election campaign in Perth. The council results will be a vital test as to whether they can make inroads against the SNP in an area that voted strongly against Brexit.

West Midlands Mayor
Polling is neck and neck in the mayoral contest but if Andy Street wins the West Midlands for the Conservatives it will be the headline of the night. Labour has dominated council elections in the West Midlands region in recent years and won last year’s police commission poll by 26 points. A Tory victory would therefore be a severe blow and intensify the sense of gloom among local Labour MPs that parliamentary seats are now at risk. A win for Sin Simon, on the other hand, would give Jeremy Corbyn a major boost ahead of the general election.

Could a local election disaster trigger a Labour implosion?

Labour MPs are already in despair at the state of national polls. A terrible night of local election results just a month out from the general election could trigger political meltdown. Even today there is talk of emergency action to try and oust Corbyn, with some recalling that George Lansbury stood down as party leader just a month out from the 1935 election. Labour fought that contest with Clement Attlee in charge. But a similar change now seems an unlikely prospect. Realistically it would require Corbyn to fall on his sword and the NEC to appoint another leader, probably Tom Watson, in his place. However Corbyn has to date resisted all pressure to throw in the towel, stiffened by hard left supporters who are determined to retain control of the party.

Since the failure of the leadership challenge last year the majority of moderate Labour MPs have decided to follow the “Golding strategy” – so named after the right-wing Labour NEC member who advocated that the Bennite 1983 election manifesto should be adopted by the party without challenge; in order that the left would be so tarnished by its rejection at the polls they would be permanently discredited, enabling political reconstruction to take place.

However, if the local elections on 4 May point to a seismic cull of Labour MPs even before the 2017 Labour manifesto has been published, many Labour candidates may decide that there will be nothing left to rebuild. In that event we may see a more organised and widespread trend of Labour candidates actively disowning the party leader and the national manifesto. That process has already begun, with various Labour parliamentary and mayoral candidates issuing personal manifestos and overtly distancing themselves from the Corbyn leadership. Unless there is a remarkable turnaround in the next six weeks, it would appear that things can only get worse for Labour.