Does the warning light come on when its very cold? This morning (bloody freezing) on the way to work my brake warning light came on for a while, after about 10 mins it went out and hasn't came back on. I noticed a slight knock as i pulled away as if the handbrake had siezed slightly but the pedal was fine and the brakes worked fine. Am i being paranoid?

There are a couple or three things that can cause the warning light to stick on. Either a low fluid level, sticking fluid level float or possibly a sticking/dirty handbrake switch.

Have a look at the fluid level first and see what that tells you.