Nothing to do with security
I think you all must remember that the UK's security regulations are primarily intended to protect govenment ministers and civil servants from critsisum in the press.
A whole raft of the regulations are utterly useless from a security point of view and some are counterproductive but even if the minister in charge can see this he won't do a thing about it because some one with a financial interest in the yogurt police will leak a story to the press that he is being weak on security.
The sad thing is, if you put the minister the civil servant and the journalist in a room together they could probably all agree that the whole security situation has got kind of silly. Unwieldy, inconsistent and way out of proportion to the risks.
But then they return to their desks and realise they have careers to preserve. No politician ever got fired for a "tough on terror" attitude. No journalist even got fired for being tough on politicians and civil servants. And so the whole thing staggers on like some sort of headless chicken.