There are no signs of coolant leakage and engine oil is clean (changed every 10k miles), I've had the rad pressure tested and pressure maintained.

My mechanic is of the opinion that it is a cylinder head and/or gasket problem

So, where do I go from here? Bite the bullet and get the head/gasket investigated at a Ł1000+, ( diy job?) or trade-in?

What is 2000 Avant Se worth?

Advice very much appreciated