Apparently the banks fraud department notify the police as the bank are the victims.
It still amazes me how efficient they are detecting fraudulent activity- we were ripped off a few years ago whilst we were in Spain and credit card cheques ( dreadful things) were being used in the UK to buy a car. The computer picked up that the cheques had been signed the same day as cash withdrawals were being made in Barcelona- by us. However these may only be the ones we know about, so we are now intent on checking every statement that comes through the door.