As Jason said I replaced the part of the catch in the boot lid without adjusting anything and it is now working fine. I can not for the life of me see anything wrong with the old catch though. The spring is ok and it seems to latch - and I cant get it to release without pushing on the release lever. Interestingly I can now slam the boot and it catches whereas before it would only catch if you closed it gently. I guess it will remain a mystery, Thanks for your answers guys. David.