Thanks for your commnents.
What i can not understand is why the NHBC after inspecting the home on 3 occasions July 2002, June 2003 and June 2004 have never accepted the nail popping as a defect or even told the builder they should investigate the cause of it. NHBC always takes the word of the builder the homeowner has no chance.
http://www.persimmonatmaplelodge.co.uk/