Happened to me a few weeks ago on my BoS visa debit, was paying for my girlfriends phone bill on the phone when it got rejected. Phoned up my bank to make sure everything was peachy, he said it was. Later that day going home for the dentist, tried to buy a train ticket from a machine, said sorry out of paper hmmmm....
Came back from the dentist the next day (1st September) and luckily I checked my account to see if my rent had came out properly due to a muck up last month by the property company and there it was, two random payments one £110 tmobile 0845 payment and £200odd payment to a tent website.
Phoned up the bank right away, canceled my card within seconds, then the guy looked into it further and went onto explain they had picked up and blocked a possible fraud payment a day or so earlier, so as I made sure there were no other bad payments he sorted it out and put me through to fraud, who again were very nice and helpful.
Popped back to my parent/billing address on the 8th (last week) signed the fraud papers and got my new card and today I got a txt from my Mum saying she just got a letter for me from the bank saying all the money was back in my account.
Anyway to sum a long post short. Bank of Scotland have very nice phone staff and even for a debit card they look after you well, Mums are good to calm you down when you notice several hundred pounds are missing from your account and people who steal card details to buy a tent are *****.
EDIT: Also I still have no idea how my card details where stolen, only recent things I bought online had been through a very very trustworthy (cant name competitor) site and paypal, hadnt used a cash machine in yonks and the only place I had used my card was at the supermarket. The only things I could think off were a virus (all PC's in the house have since been cleaned and formatted) or that they were stolen a while ago but not used until now.