Checked my coolant level on Monday after driving back from Scoobyfest on Sunday, header tank almost empty and area around coolant resevoir damp with coolant (but coolant resevoir still at correct level). No white smoke from exhaust, no change in water temp on guage (always reaches just 1mm under halfway once warm), no water in oil or change of oil level.

Topped it up again and after 20 miles today it is half empty again and also damp again around the the coolant resevoir (again resevoir level is OK).

Does this sound like faulty head gasket pressurising the cooling system?

Am I taking the family to Cornwall on Friday in a crappy hire car and facing another massive garage bill??.......