Officially, the Government claims not to comment on "security measures", even when doing so would not actually compromise security, but would just highlight an ongoing scandal which bureaucrats do not want to take the blame for.
An example of this is the question of Visitors' Passes to the Houses of Parliament raised as a Parliamentary Question:
"HOUSE OF COMMONS COMMISSION
Grey Visitor Passes
Norman Baker: To ask the hon. Member for Roxburgh and Berwickshire, representing the House of Commons Commission (1) how many grey visitor passes have been issued to visitors to the parliamentary estate since they were introduced; 
(2) how many grey visitor passes issued to visitors to the parliamentary estate have been lost since they were introduced; and what efforts have been made to recover them; 
(3) what measures are in place to ensure that grey visitor passes issued to visitors to the parliamentary estate are successfully retrieved from visitors when they leave the parliamentary estate. 
Sir Archy Kirkwood: It is not the practice of the House of Commons Commission to publish details of the operation of security arrangements on the parliamentary estate.2
However, the BBC reports that:
By Nick Assinder
Political Correspondent, BBC News website
Daily despatches from the House of Commons
1230 BST 1 November
Security in the Commons has become so tight of late that not even the mice can get in without a pass and a body search. One of the most obvious changes has been the requirement for all visitors to wear passes around their necks with a large black V on them.
Trouble is, they have become sought-after souvenirs for tourists and other casual visitors.
So much so that it is believed up to half of them never get handed back, but simply go missing.
Surely there must be ways of getting them to self-destruct after a period of time!"
Where are the turnstyles ?
These do not have to be full height revolving door "man traps" if they are supervised, like the London Underground ticket barriers which are so familiar to most visitors to the Palace of Westminster.
What is the point of issuing passes if, during a security or fire alert or evacuation, nobody can tell exactly how many people might still be trapped inside the building ?
Even if, in the future, every visitor had to show Biometric ID cards or Passports to get a Visitor Pass, the basic security problem would remain.