@Worldgonecrazy and @bakingcupcakes
Maybe the Prime Minister / government said May but had actually already planned to bring the date forward to make us all so happy to be free we don’t notice what a shit show we are being freed into?
I'm almost certain this is the case. First rule of negotiation: always demand much more than you hope to get. He will indeed be able to move things earlier to appear to be reasonable, so people will love him again, and so that he can say "the new variants weren't as deadly as we thought", to bury the idea that they ever were. (I suspect it was a lie, or at least an exaggeration.) It would tie in with them deliberately underselling the vaccine so people don't fight over it, so he can say "looooooooooook!!! The vaccine is working!" when it suits him. Also, if the public gets restless, and riots start to look likely, this can be quelled by easing something to keep the plebs happy.
I think someone's been having serious words with Saint Boris about not saying optimistic trite this time round, like the original "we can turn this virus around in twelve weeks", which he hopes we've forgotten, so he's keeping his cards much closer to his chest this time.