Hi guys. Sorry to be back with another problem.
The car has decided to start drinking coolant again. I presumed it was the head gasket going but there's so much water going now I'd be surprised if it would run at all. It's getting through a third of a bottle of coolant a day, it's going within maybe 20 miles. If that was head gasket, then the clouds of smoke out the back would be huge if the engine ran wouldn't it? There's no bubbles or oil in the coolant either or water in the oil. I"m guessing it's a leak somewhere but even after sitting overnight, the system is still pressurized. Does this suggest a leak somewhere? Engine never overheats but is in need of a new thermostat. It only hits maybe 80-85 on the gauge max. I've just been out to top it up again now and something caught my eye. There's a damp patch near the bottom of the engine, by the oil filter. Not sure what it is but grabbed a photo anyway.

EDIT: That's the right colour for the coolant now I can see it on the computer. Couldn't tell outside without the flash.
Have you guys got any ideas? I need to drive the thing to London and back in a day next week so I've got to sort it ASAP.
Cheers.