The "official" way of dealing with lost property in the UK is to take it to your local police station. If no-one claims it within 6 weeks, you might be able to keep the item. I certainly remember doing this a few times when younger. Not so sure many people know this nowadays.
Anyway, my mother lost her purse a few months back in the small town in Scotland where she lives. Someone suggested she try her local police station (actually not so local any more thanks to the current government having closed over 600 police stations[0]) and lo and behold someone had handed it in there!
[0] https://www.thetimes.co.uk/article/600-police-stations-shut-...