My other car is a MINI!!!!
Epic bump here, google brought me to this thread.
I have this problem too, and I've still not solved it after months of searching!
I contantly get the brake light warning light come on, to say my brake lights are broken, but they're working just fine :S
So far, I've changed all the bulbs, I've changed the bulb holders in the back, and I've changed the brake light switch on the pedal, and it's still just as bad. Sometimes it won't come on at all, but this is very rare. it usually comes on and off constantly every 30seconds - 1 minute the entire time you're driving.
it really does drive me mad! Anyone got any suggestions? I was sure it was the switch at first, but its obviously not