Some great suggestions here - thanks guys. I will pop in to Halfords (uk car products chain bit like pep boys i guess) and pick up some cleaning products and give it a go. I don't have a wet vac but I think you can buy some foam type stuff that you can spray on the carpet and mats and then vacuum up when it goes dry. I'll try to find some of that. I'll also stick some bicarbonate of soda down and hoover that up the next day.

For the seats I think I will give the meguires gold class cleaning and conditioning products a go. I've heard good things about them.

I'm going to use a can of comma air con cleaner which apparently can clean out the smells in the air con system - figures that the cigarette smell will be stuck in there.

I've read about the dryer sheets in a few places now. I'll be using those liberally around the car once the clean has been done.

The one area I'm a little confused about is headling. I know it's dangerous to get headlining wet. Would the carpet cleaning foam that dries and which you then vacuum be ok for the headlining?