which wire goes where on two way switched light?

I am replacing a light fitting in the sitting room which has two way switching. I have, at the ceiling, 3 red wires, 3 black wires (one of which is permanently live with both switches in the off position) and 1 earth wire. The light fitting block has marked 1 live, 1 neutral and 1 earth position.

What goes where? At the moment, when I put the fuse in the light comes one until one of the switches is used and then it goes off and won't come on again!!

Help!

Harry
June 2008