Have had a look with a mate and after satisfying myself that it isn't a head gasket failure (my last car was a K series 1.6 Rover 200) I discovered two other possible sources of the leak.
One is that the area around the steering assist tank is pretty gunky so it looks as if it has been blowing stuff around.
The other is a tube that connect to what I think is the intercooler (sits on top of the engine?). The tube connects right in the center front and isn't held on by anything, there is oil around the connection and it looks like it has been dripping down onto the engine, then undernieth and dripping on the floor around the same area where the patch has developed.
Obviously I'm not too familiar with a diesel + turbo engine so would appreciate any advice, ie is it ok to drive, where to look for oil levels that supply this pipe etc!
Thanks! Rich.