A display at Tate Modern has been withdrawn following a visit to the gallery by officers from the obscene publications unit of the Metropolitan police. The display features a naked photograph of the actress Brooke Shields. The pop artist Richard Prince first used the image in 1983, by which time Shields was a household name, but the photograph itself was part of a set taken by Gary Gross seven years earlier, when she was only 10. Shields's mother authorised the shoot for a fee of $450, and the photographs appeared in a Playboy Press book entitled Sugar and Spice. In 1981 Brookes launched an unsuccessful legal action aimed at preventing further usage of the pictures.

The story reveals the gaping divide between the culture of art in 21st century Britain and the culture of policing. On one side the curators, who talk like this: "When Prince invites us to ogle Brooke Shields in her prepubescent nakedness, his impulse has less to do with his desire to savour the lubricious titillations that it was shot to spark in its original context … than with a profound fascination for the child star's story."

On the other side the police, who talk like this: "The officers have specialist experience in this field and are keen to work with gallery management to ensure that they do not inadvertently break the law or cause any offence to their visitors."

You wouldn't go to an art gallery or a police station for beautiful prose; nonetheless you wouldn't mind a bit of sense. The curators should admit that, whatever Richard Prince had in his mind when he created the work, lubricious titillations are precisely what it will spark in many viewers. On the other hand, the police have no business whatever ensuring that galleries don't "cause any offence to their visitors". Who gave them the idea that gallery management was part of their job description?

Well, we did. Or, rather, parliament did, acting in our name through the "extreme pornography" clauses in the Criminal Justice and Immigration Act 2008. As Julian Petley showed in the March 2009 issue of Index on Censorship, these new measures remove the old distinction in the Obscene Publications Act 1959 between "pornography" and "literature", leaving the police free to meddle in the moral maze of contemporary art. They empower the state to ban material which is "grossly offensive" or "disgusting". There is no defence of artistic or cultural value.

This story breaks on the same day as news that the most banned books in American libraries include JK Rowling's Harry Potter books, Philip Pullman's His Dark Materials trilogy (at number two) and the true story of two male penguins at a New York zoo who form a couple and are given an egg to raise – And Tango Makes Three (at number one). Attempts to ban these books have been led by religious groups, who are, no doubt, deeply "offended" by their content, whether on grounds of sex, witchcraft or heresy.

The withdrawal of Prince's work from Tate Modern is too close for comfort to the populist, mob-ruled approach to "gallery management", which the Metropolitan police now seem to be espousing. I'm not particularly comfortable with this picture being displayed in a gallery that attracts huge numbers of children – particularly given Shields's own objections. But I'm rather more uncomfortable with the idea that the police are equipped to curate art exhibitions.