The acid test is to check the coolant for oil, and vice versa. If it's just on the filler cap, and no evidence in the other two, chances are it's just poor breathing. Could be a blocked breather pipe somewhere. No need to panic yet.

Edit - any white smoke under heavy throttle?

Or lots of white smoke on a cold start, accompanied by a lumpy engine when cold? And how about columns of very small bubbles - like the fizz in lemonade - visible in the header tank? I had both those in addition to 'mayonnaise' in the oil filler strainer of my Peugeot 505, plus an increase in oil level indicated on the dipstick associated with coolant in the sump.

Cheers chaps. He's talking about selling it now. We won.

Another potential Octavia owner?

Rob, i was referring to the warning light on Rich's neighbour's car

Figured you might be, but wasn't going to leave it to chance...

Get the Beetle hooked up to VAG-COM though, it might just be a temperature sender fault...they don't seem to like hot/cold/humid/dry weather, so it might be a "false" alarm...

Rob.