Meow, yes I am preheating it. For at least 15 minutes, usually more though.

Sepata - its a Westinghouse Kimberley, from what I have read on the internet it seems to be a problem across the board.

Astrid - thanks, so far cooking much higher in the oven has helped. I will definitely see to getting a thermometer to check out what it is actually doing though.

Very frustrating!