Turns out that loss of coolant was due to the head gasket.
How am I sure ?
Coolant has completely disappeared from the reservior, oil has gone watery and looks like chocolate milkshake, white smoke pours out the exhaust and it barely idles and misfires badly.
I have recently invested in an '02 Saab 9-5 2.2 TiD so I still have an economical powerful saloon to drive, however I do miss the Xant's 2.0 high RPM power
Oh well, in a few weeks she'll be back on the road. Though it is going to be a hell of a job to fix, considering I kept driving it with 40% anti-freeze in the oil before I realised...
So possibly the whole engine will need to come out and get rebuilt. First of all though I'll change the gaskets and spark plugs then see if she runs alright, if not, the engine's coming out!