Dear Mary: is it OK to drop by to see a friend’s garden during the pandemic?

Q. I own a small, somewhat shabby and antiquated but well-located flat in central London which I have been happy to lend out to friends as I wasn’t using it much myself. No one was there during lockdown but four separate people stayed for various lengths of time just before. No one paid to stay there and I wouldn’t have wanted them to, but arriving there myself this week, for the first time this year, I found a vital piece of equipment broken — the glass jug of the ancient coffee machine. It’s not the cost (and difficulty) of replacement which annoys me, but the thought that one of my friends could be so inconsiderate as not to tell me either that they had broken it, or that it was already broken. It’s no fun not being able to make coffee when you need some. How can I find out who did it without offending the ones who did not?
— R.P.,