Cooling fan stays on

After 3 years of behaving normally my 1995-reg V12 gave me a niggle today. I had been out in quite warm weather (I live in France) and everything seemed normal, I wasn't surprised to hear the cooling fan running when I stopped because I had been in traffic. Then I stopped to do some shopping and when I got back to the car the cooling fan was still running. I drove home and the fan must have stayed on because the needle was slightly lower on the 'N' than usual. I left it for a while after I parked at home but it didn't cut out. Eventually I stopped it by pulling the fuse.
Any ideas? I hope it's a faulty switch or relay. Can someone please tell me where the temp switch is and which relay is which? I have the Kirby Palm book on pdf of course but I just hoped this might be a pretty common niggle.
Thanks in advance...