Farage has proposed a so called "Leave Alliance" this morning and given Boris two weeks to respond before putting in his nominations. I think there is no chance of Boris going for that. It would require him to scrap the recent deal he negotiated with the EU, which he isn't going to do. If he did it would likely split open the Conservative Party all over again. It would also probably drive some potential Tory voters into the embrace of the Liberal Democrats.

So the Brexit Party is likely to field candidates in all constituencies in England, Scotland and Wales. This may split the Leave vote in marginal constituencies but on the other hand may take plenty of votes off Labour in the north. It is anybody's guess as to which factor will end up being the more decisive.