Some interesting comments on the NT stance at the site below - an interesting sire that seems to focus on general copyright issues for professional and semi-professional photographers.

http://copyrightaction.com/forum/national-trust-byelaws-in-a-twist

Also link below gives details of the NT's complaints procedure :-)

http://www.nationaltrust.org.uk/main/w-global/w-contact_us/w-complaints_procedures.htm