dvds2000
Gone But Not Forgotten
Thanks again, Col.
Garage chappy says it's the electrical component of the valve that's "gubbed" so it's definitely a new valve that's required. He said for him it's about £170 for the part and maybe £20 for fitting plus VAT, so about £225. I'm not sure I should spend that on a car of its age and mileage. He suggested ebay too and said it's a very easy DIY job.
Ebay here I come...
I would try there too. Its what its worth to you though, if the car is reliable and getting used, even £225 isn't much to spend to keep it on the road another year or two.