Helloall, just an update. We go away tomorrow so I decided to get the van in the garage to give it a once over. They tried all the stuff mentioned on here including stripping the carb down as it had a slight leak on it.
Anyway, it's bad news

they did a compression test and all four cylinders have low compression: 130psi, 120psi, 110psi and 108psi.
So engine rebuild may be in order, or drop a good DG engine in Mick has one in the for sale section), or go down the Golf AAG / Subaru root. Lots to think about but at the minute i'll just let it run and get worse, if anyone has any thoughts or advice that'd be good to hear.