Despite Theresa May’s falling support in London, Jeremy Corbyn might be disappointed in the local elections

One reason for this divergence lies in the way the Brexit referendum has helped reshape Britain’s electoral geography

The local elections that take place in much of urban England on Thursday have been widely presented as a severe test for Theresa May. Failure to retain control of two Conservative citadels, Wandsworth and Westminster, has been portrayed as a potential precursor of renewed restlessness about her leadership on the Tory backbenches. However, this week’s ballot could prove as much of a challenge for Jeremy Corbyn as it does the prime minister.

Much of the speculation about the elections has focused on the contests in London, where all of the seats on the capital’s 32 boroughs are up for grabs. London has become increasingly difficult territory for the Conservatives, not least thanks to the party’s difficulty in appealing to the capital’s growing ethnic minority population. (The party’s vote fell by nearly two points in the capital in the last general election, even though it was increasing by nearly six points across Britain as a whole.) Meanwhile, polling of voting intentions for the borough elections suggests there could be a swing of some 4-5 per cent from Conservative to Labour on Thursday.

However, there is another set of elections taking place on Thursday – in 118 district councils outside London, including in most of England’s major cities from Plymouth to Newcastle. These contests look less exciting because, in most cases, only one third of the council seats are available, inevitably making it less likely that control of the council will change hands. Yet they may prove the more important guide to the standing of the parties, 12 months on from last year’s snap election.

Most of the seats being contested on Thursday, both in London and elsewhere, were last fought over four years ago, when the local elections took place on the same day as elections to the European Parliament. Commentators took the parties’ local performance and applied it at a national level: Labour was estimated to be a couple of points ahead of the Conservatives, similar to the position in the opinion polls at that time. This is the baseline against which seats and councils will be gained and lost on Thursday.

Crucially, it is a better baseline for Labour than is to be found in the Britain-wide polls at present. These polls, on average, put the Conservatives narrowly ahead of Labour. So, if Theresa May’s party is losing ground in the capital, it must be gaining ground elsewhere.

One reason for this divergence lies in the way the Brexit referendum has helped reshape Britain’s electoral geography. In last year’s general election, Conservative support typically decreased in those places that voted heavily for Remain, whereas there was a net swing from Labour to the Conservatives where voters had heavily backed Leave. A similar pattern had emerged in the county council elections a few weeks earlier.

That pattern largely explains why the Conservatives did so badly last year in London, which voted by three to two in favour of Remain, and why the party is still struggling in the borough elections now. But outside of London, Thursday’s elections are taking place in districts where, on average, only around 45 per cent voted Remain, a figure that matches the outcome of the EU referendum across provincial England as a whole. Making progress in these elections looks like a much tougher test for Labour.

Given how well entrenched Labour is in many of the councils it currently controls, a modest swing against the party outside of London could leave its tally of controlled councils largely undiminished. But any such movement could cost it gains that the party might otherwise be expected to make, such as in Leave-voting Amber Valley, Kirklees and Walsall. At the same time, a swing in their favour could help take the Conservatives over the line in, for example, Basildon, Pendle, Peterborough and Rugby, thereby helping to counterbalance any losses the party suffers in London.

Even if there is a swing to Labour in London, it might not cost the Conservatives that dearly. The only low-hanging Tory fruit available for Labour to pick is control of Barnet. However, at 15 per cent, the borough’s Jewish population is the largest anywhere in the UK and Labour must be concerned that the row about alleged antisemitism within its ranks might cost the party dear.

Otherwise, Labour needs substantial swings – of 7.5 per cent or more – to make any council gains. Such a swing is, perhaps, more likely to occur in Wandsworth or Westminster than in another of Labour’s targets, Hillingdon, where, unusually, Leave came out ahead. But, even so, picking up either of the Tory citadels looks like a tall order. Jeremy Corbyn has to hope he does not look rather embarrassingly empty handed when the results come in on Friday.

John Curtice is professor of politics at Strathclyde University