Well I've been doing some digging and diagnosing in my spare time and I've refilled the coolant, now last time I checked it was 3 days before I noticed it was dropping, then I checked the other day and in 3 days it had dropped but I'd only done 186 miles, so theoretically it would drop again if I drove a similar amount of miles (provided it's a consistent leak) but yesterday I filled up the coolant and drove 200+ miles to Herefordshire to visit family and the coolant level hasn't moved, when I took the expansion tank cap off to refill it, it was only hand tight so I assume the guy I bought it off hadn't done the cap up til it "clicks" and the coolant was evaporating over time, and also it couldn't pressurise properly hence the coolant warning. Since topping off the coolant and driving it 200+ miles I've had no warnings or coolant drop so maybe this was the issue all along. Still got the lumpy idling and smoke but I'm sure I read somewhere that the 2.0td had an injector recall in 2012 for overfuelling or dodgy injectors, I had a pile of paperwork and service history with the vehicle but nothing to mention it ever having the recall done.