My suspicion that Taking Liberties, the British Library exhibition now in its final week, would be a slightly sanitised version of the story of liberty was borne out by a visit last Tuesday. For one thing there is no record of the nearly 30 acts and more than 50 measures that have been used by Labour to strip our stock of liberty, which is perhaps understandable given the library is staffed by civil servants. The show draws a veil over developments after the introduction of the Human Rights Act and implies that we have achieved a state of blissful and unequalled freedom under the current government.

I left dissatisfied but then fate, or rather the Metropolitan police, intervened to provide a living supplement to the exhibition. Within eight paces of the entrance to Taking Liberties two officers, a man and woman, had stationed themselves inside the library and without the slightest sense of irony or trespass were stopping people to ask their names, contact details and height under terror laws.

I would have taken a photograph with my phone but that has been made illegal so I watched while a stream of utterly ordinary-looking people were questioned. I asked one man whether this was usual in the British Library. Yes, he said, it was well known that the police used the library as a convenient means of boosting their stop and search quotas and balancing the number of black and Asian people stopped in the street with the white people in the library.

I cannot say whether this is true but I saw nothing to disprove it while I looked through the postcards. He added that the police favoured the library because at the entrance everyone's bags are given a cursory search. So the police had only to stop people, not search them, and this saved time for a pair of busy constables who were clearly in a hurry to get the names in their notebooks and move on. The idea that this is an effective anti-terror measure is ludicrous. It looks nothing but a complete waste of time and an insult to innocent members of the public, whether black or white, who are inconvenienced and made to feel under suspicion by a law that is apparently being abused.

That this is going on within a few feet of the Taking Liberties exhibition is a comment on our society's strange double think about liberty and also the fecklessness of the library, which allows it to happen seemingly without complaint.

I asked the library to comment on this story but have yet to hear back. Perhaps the press office would like to write here. Meanwhile the board of the library should of course take this up at its next meeting on 24 March, for the library appears to being used by the police in a way that infringes its readers' rights.

As to the exhibition, you should give it a miss unless you want to see the terror laws in action. But I can recommend a short video clip of Lord Carlisle, formerly Alex Carlisle and now the government's "independent" adviser on terror law, in which he suggests that it is quite reasonable to lock up people for 42 days without charge. The finest satirist could not make up my afternoon in the BL.