No clue but you could always ring BT to confirm, if there is accidental damage owing to you removing it you may get in a spot of bother

I have often lifted covers. The only time I wouldn't is if they have a police security-check seal on them (as they often do immediately before major public events). If the installer doesn't want them lifted, they should fit ones with locking devices, or at the very least put a sign on saying 'Private property do not lift". If I'm doing a site inspection for any purpose I always lift every cover I can find and can safely lift in the immediate vicinity and photograph what I find inside. It has never got me in trouble yet.