Hi thanks for the quick response

I changed the spark plugs last weekend and the old ones looked pretty good, a bit of an orange colour on them was all. Haven't seen any smoke coming from the exhaust, not on cold start up or when I put my foot down. I had a look at the radiator cap and couldnt see anything (i checked straight after a drive) but it could be jus a small leak and evaporating away whilst i'm driving

No white mayoinaise in the oil filler cap either. Really stuck for ideas on what it could be

got it booked in to a garage on friday so i'll keep you posted, fingers crossed! lol