I’m an avid reader of the MoneySavingExpert.com forums.  Today I came across this one:
http://forums.moneysavingexpert.com/showthread.html?t=1829957

I’ll copy and paste the main bit from it here:

My brother was on holiday in Jersey and on the last day he went to an ATM to withdraw some cash. Just as he was about to insert his card the machine shoved out a large wodge of notes. There was no-one around and he had not noticed anyone walking away from the ATM when he arrived, so he grabbed the money and shot off. He met his wife and friends and they counted the cash – it was £300!!

Now I (and I’m not the only one) posted that I would probably keep the money.  First, I would check and make sure that the previous user of the cashpoint wasn’t still around.  If efforts to locate them failed, then yes I’d keep it.  Does that make me a bad person?  What do you think?

I was in Shepherd’s Bush a couple of months back and I had unknowingly dropped my debit card on the ground.  A guy came running up to me and handed it back to me.  I was very grateful for it.  So I would definitely try and find who it belonged to first.  But If I couldn’t find the person, then yes I’d probably keep it. 

Of course that situation is slightly different - the debit card has no real value to the finder.  If I had’ve dropped £300 on the ground, I would of course be happy if the person returned to me… but would I expect them to do it?  No I would not.  Perhaps I’ve been living in London too long, and my faith in mankind has diminished somewhat.

When I was 23 (in 2003), I was walking to The Hilly (Hillcrest Tavern – a popular student hangout near Waikato Uni) from my house in Albert St (about a 20 minute walk) and I found NZ$75 on the ground on Wellington St.  Was I going to hand it into the police?  No way!