I left a job and they accidentally paid me an extra month. I got a letter asking for it back, but they never followed up.
It turned out the accounts guy was robbing them blind(former colleague told me), and also not doing his job properly.
I think my overpayment got lost in the xxxx storm.
Same, i left a job and got full holiday pay, 1 extra month salary and they didn't follow up on the "Buy a PC through your workplace" scheme they had going. I got myself a q9550 CPU, 4870 GPU and other good parts....never had to pay out of my own pocket for it lol. The scheme was a salary sacrifice thing but they never bothered starting to take it off me before tax, so i never told them.
They also had a Cycle to Work scheme too and I got 2 bikes from them at about 1,000 that they never asked for either.