Originally Posted by IAN-UK

Maybe i haven't understood the situation fully: you don't reveal the airline you were traveling with, but I'm guessing it wasn't Turkish. You should contact your airline about your bag. It's likely it is with that airline's baggage agent at Heathrow as unclaimed baggage. Unless, of course, someone carelessly took your bag by mistake .......

Normally they courier a retrieved bag to you. But where the passenger abandons his/her bag on the carousel they may expect you to return to the airport to pick it up.

Quite separately you really should do everything you can to reunite the bag you took from the airport with its owner. If there is an ID tag with contact details then use those to establish contact with the bag's owner. If that isn't possible then you need to either return the bag to Heathrow (there's a baggage enquiry phone in the arrival area) or phone Turkish Airlines 020 3991 1993. Keep it simple - they are not interested in your bag, just tell them you took the bag of one of their passengers from LHR T2 by mistake.