Further updaye, since finding the manual in the glovebox it pointed me towards the battery/alternator with that warning light and the belt driving the alternator has gone! So I will be calling the AA man to get me home in the dark. Does anyone know what else tis belt drives? I am a little concerned that the engine got very hot and the turbo was not kicking in.

Probably the water pump. With no water circulating the engine will overheat and the temperature gauge will rise. Eventually it will get so tight, it will start to seize and feel down on power, almost as if the turbo isn't working!

Thanks for the replies. Was moving at a steady 50mph, weather was cold and rainy was not in traffic thankfully. Was probably 10 miles at the most. I think it may drive the water pump too. I also think you may be right that it went into a limp mode. Engine was not tight at all, just lacking in power. Revs were slow and steady just took forever to get anywhere.