HSBC haven't got back to me in time, despite me ringing again today, so there's no way we can exchange on the 23rd or 24th, and hence we can't move on the 24th and won't be there on the 25th, so I've emailed to cancel our removal van (for now) and try and arrange that our fridge can be delivered on a later date instead. And having done these things I feel a lot better, especially as Kevin the landlord has said he really doesn't mind at all when we move in and Peter moves out so long as he can come and read the meter on the day. Thankyou Kevin, you have made me a lot less stressed. If they get it sorted tomorrow or Friday we might be able to move out on the 25th or 26th, which means Peter can move in pretty much as planned. If not we're fairly sure we can come up with contingency plans. The world has not ended.
I wonder if they'll ring me back tomorrow? - Edit: ha! They didn't even have a note on my file that they were supposed to call me back.