Three of our last five weekly Local Government by-election summaries have reported the Liberal Democrats gaining seats.  These results are not an infallible guide to the current political mood, since much depends on where the elections are taking place, and their distribution is arbitrary.  But there is none the less no doubt that Brexit has opened the door for a yellow revival.  The Conservatives have become a party of Leave.  Labour is divided.  That leaves Tim Farron’s party to mop up the proportion of the 48 per cent who are unwilling simply to go along with Brexit, and feel so strongly about it that they will protest at the ballot box – as they did in the Richmond Park by-election Research in the Daily Telegraph this morning suggests that this percentage is about 48 per cent of the 48 per cent.

Theresa May’s national lead over Labour in the polls – 16 per cent according to the most recent one – is masking this local Liberal Democrat revival.  The latter is likely to turn out to be one of the main stories of May’s local elections: the first real electoral test, remember, of her Government’s popularity.  They take place in exactly a hundred days time.

There are three main obstacles to Farron transforming this protest vote into seats at the next election.  The first is the change wrought on the seats it holds, and others it will target, by the boundary review.  However, Parliament is yet to have its say on the matter, and an election could come before 2020 anyway.

None the less, it is reasonable to assume that its date will be as planned, and that the review will pass.  The second difficulty for the Liberal Democrats is the distribution of the Remain vote.  It was concentrated in London and its commuter belt.  But the yellow vote in most of the capital is weak, and the blue one just outside it is strong.  The final problem is that anger over Brexit may have faded by 2020.  If so, the Liberal Democrats won’t make much of an advance on the eight seats they hold.  However, if Britain leaves the EU in 2019 as planned but without a deal, and there are problems in the implementation of MFN, the Liberal Democrats will surely gain seats.  And if Corbyn is still Labour’s leader, Farron will be able to suggest that the Conservatives will win nationally, so soft blue voters unhappy with the outcome of Brexit will have nothing to lose by voting yellow in their own seats.

Under these circumstances, the Liberal Democrats would be most likely to gain constituencies that the Conservatives took from them in 2015 and where the Remain vote is very strong.  Then throw in a few Labour seats where the last applies too, such as Cambridge.

What are its Tory equivalents?  There is Bath – another university seat.  There is Lewes.  Above all, there are those seats in the south-east of Greater London near Richmond Park – Twickeham and Kingston & Surbiton.  But there is not a large number of blue-yellow marginals where the majority is very small and the Remain vote was very strong.