The Queen could do it.
Or, rather, try to do it. It's a fascinating aspect of our Constitution that only convention* prevents the Queen from trying to force a PM to step down. I suspect that the Courts would be obliged to step in, and there'd be uproar, but, still, as I understand it, there's no legal mechanism that yet exists that explicitly stops the Crown from trying.
This isn't meant to be serious (see the footnote). It's irritating that ministerial accountability simply doesn't exist under the current Government -- I'm struggling to imagine a clearer breach of the Ministerial Code of Conduct than breaking rules you yourself had laid down -- but unless the Tory Party itself decides to force Hancock out then he's clearly staying.
*Legally, that is; the Queen also wouldn't even dream of trying this anyway.