People may not know this but its kinda related, there is a crime called theft by finding (or something similar), so if you find something it is not legally yours to keep. finders keepers is a playground myth. You are meant to hand it back to the rightful owner, this could be the bank in the case of bank cards etc, or simply hand the property in at a police station. After a set amount of time (6 months I think), if no-one has claimed the property you do have legal claim to it.
The reason I know this is because someone stole my phone once, he claimed in his defence he found it in the cab, he therefor got cautioned with the offence Theft by finding. The other stuff I know because I'm always handing lost property in at cop shops (I have 48 hours from finding it to either return it to the owner or hand it in at a police station), I''ve been offerd a few things back after the 6 months, none of which I wanted