Yes, this is their one ‘legitimate’ play to stop Brexit. If Labor decided to make this a ‘pseudo-referendum’ on it (unlikely, I think, but not impossible) and won (very unlikely) a legitimate constitutional case could be made that ‘the people have spoken and changed their mind’.
Of course, this would also require the EU nations to agree to allow Britain to back down.
So it could be very interesting.
I can’t really see it happening, but I can certainly see people trying to make it happen.
Labour can’t realistically make this a ‘pseudo-referendum’ on Brexit. It would look farcical them taking that approach because of the divisions in their own party on the subject. Nobody thinks Corbyn is enthusiastically pro-EU - McDonnell even less so. They were so anemic with their support for the Remain campaign that such a stance would not be plausible.
The Lib Dems will certainly run almost entirely on an anti-Brexit platform. They should make significant gains (especially in Cornwall and the West Country) but its hard to see past a Tory increased majority.
Labour are hopeless at the moment and the Conservatives have the largest lead over them since 1983. They are sitting ducks hence May's opportunistic decision to call a General Election even though they are only supposed to happen once every 5 years (the next one was to be in 2020).
The only political party who will reverse Brexit are the Liberal Democrats and they are the fourth largest party after the SNP and so have zero chance of forming a government. There is no way to reverse Brexit now short of a revolution. Some might call that a failure of the democratic process given that the government seems to advocate a policy of Brexit at any cost!