Hand it in definitely.
Once found £200 all tightly bundled up, & I just knew that it was someone's pension as it looked neat & tide together. I took it to the police station, after a couple of months I got a call to claim it back as no one had reported it missing.
I donated it to Age UK. To this day it breaks my heart into pieces that someone lost that money, it's making me a bit upset again actually just thinking about it.
I think it's horrible , heartless & selfish to keep it