Politics is full of surprises, if we didn't know that already. Suddenly, after months when it seemed impossible that there would be a second European referendum, we get one. It may be called the 2017 general election, but another European referendum it will be.

This election campaign will very soon boil down to a question of whether the country wants to give Theresa May her mandate for hard Brexit. That, after all, is what the Prime Minister has called for, and she thinks she will win it. We shall see if she is right.

The wisest pitch for the opposition parties (excluding Ukip, of course) is to promise the nation a vote through Parliament or a proper referendum on the final terms of Brexit. They should make clear that the believe Article 50 is politically reversible; that whatever the UK asked for on 23 June 2016, it was not necessarily a hard Brexit with no deal in place, and a virtual guarantee that people will lose their jobs and be poorer after 2019.

Times Theresa May has said there won't be an election until 2020

May says that strong leadership and stability will be the issue under contest. One thing that could restore stability, however, is for the nation to have a say on hard Brexit. Happenchance maybe, but now we have it.

May still has a high chance of doing well, but she has given Labour, the Liberal Democrats and the SNP the one attractive policy they need – an approach to Europe that is backed by at least half the country. If I were Jeremy Corbyn, I would back that too and attempt to unite my party behind it, a single transcendent policy that could even attract business support back to Labour among those disillusioned by hard Brexit. These are strange times. Slim hopes, but something. The Lib Dems will come back, and the SNP seem to have little to fear.

On 8 June, then, the country has the chance to give its verdict on hard Brexit and whether it wants a say on the eventual terms of Brexit. After that nobody on either side should have much to moan about.

But will Jeremy Corbyn take up the challenge he ducked so spectacularly last year and actually put the Labour case for Europe, coupled with a firm pledge to allow the people the final terms of Brexit? The signs are he will indeed drop the ball. In his statement today, he said that he and his party would be fighting for a “Brexit that works for all” – pretty much the PM's own line, and one that will simply demoralise many of his candidates and campaigners.

It's unlikely, given past performance, that he will offer a firm lead, and when he fails Labour will split again, at the worst possible time. Corbyn should agree to work with the Lib Dems, in the event they have sufficient Commons seats, and work out a better line than the one Ed Miliband delivered at the 2015 election about the SNP. In other words, Corbyn has nothing to lose (and much to gain) from being as pro-European as his instincts and his spin doctors will allow.

This is not the moment to argue for socialism in one country. It is, however, Corbyn's opportunity to confound his critics and deliver for his people – including the ones in Stoke, Hull and Sheffield, who potentially have the most lose from hard Brexit.