2 things can be simultaneously true: Boris Johnson is a liar who is so completely untrustworthy that I'd check his assertion if he said the sky was blue, and in this particular case getting people boosted is a good idea.

In fact the thing he's doing to accommodate his political requirement here is softball the regulations in the hope that a panicky rush to give boosters will damp down a two-day doubling time. It won't, and he'll have to lock down yet again, far too late.