Palace of Westminster security matters are subject to bylaws that permit the Serjeant at Arms to use discretion regarding any potential breach of security matters.
EG, purely for the sake of an argument:
Anti-terror cops arrive at Palace of Westminster and say "we think the place may have been bugged, maybe by an illicit wiretap by the commander in chief of a foreign (even friendly!) state. We want to check out a potential link connected to an earlier, connected arrest" then it might be expedient for current Serjeant at Arms to say "go ahead".
-------------------
Today's Times story:
Serjeant at Arms Jill Pay: Parliament’s woman in tights
The last Serjeant at Arms, Peter Grant Peterkin, left his job after finding it impossible to work with the Speaker, Michael Martin. Last night Jill Pay was heading the same way after Mr Martin blamed her for sanctioning a police raid on Parliament. The Speaker made clear to MPs he was shocked that Mrs Pay had consented to the raid without a warrant.
Mrs Pay made history in January when she became the first woman to become one of Parliament’s “men in tights”, by taking on the 593-year-old post. Mrs Pay, who is married with two daughters, oversees Commons security and supervises 40 staff, working alongside Black Rod in the Lords.
The Serjeant’s responsibilities were downgraded by Mr Martin before she was appointed and while Mrs Pay has a grace and favour house in Parliament Street, she is believed to earn about half the £105,000 salary enjoyed by Mr Peterkin. His remit included building projects and redevelopment across the Commons estate, but his tenure came to an abrupt end in December after a protest by Greenpeace activists earlier in the year, when they scaled a crane next to Parliament.
Mrs Pay’s duties are focused on Commons security and passes. She runs Parliament’s army of cleaners and allocates offices to MPs. Her appointment was seen as a victory for “modernisers”, who wanted to end the tradition of giving the job to retired military figures. The post is a Crown appointment, and was agreed by the Queen in January, but there have been reports that Buckingham Palace was unhappy with the way the role has been diminished, and in an unusual act decided not to grant Mrs Pay “approbation” — an audience
http://www.timesonline.co.uk/tol/news/politics/article5282699.ece