LONDON, NOV. 9 -- Princess Diana took the unusual -- and by tradition un-royal -- step of sending her lawyers to court today to suppress a set of hidden-camera photos taken of her last April as she toned her thighs at a fashionable health club.

The workout-photo affair, which at first looked minor as royal scandals go, has now grown to involve matters of state. It threatens to provoke new legal curbs on Britain's sometimes unruly press, with angry government ministers saying they are now ready to consider establishing the right to privacy, which British law does not currently recognize.

The Sunday Mirror and the Daily Mirror, the papers that published the offending photos, have defiantly withdrawn from a voluntary body through which the press is supposed to regulate itself, calling its chairman an "arch buffoon." Other newspaper editors have bitterly attacked the Mirror papers for making life tougher for all of Fleet Street.

The episode began two days ago when the Sunday Mirror devoted its front page, along with six inside pages including a pullout centerfold, to pictures of the princess at a London health club called L.A. Fitness. In the photos, she wears spandex bicycle shorts and a sleeveless leotard. She is perfectly coiffed and does not appear to have been perspiring.

The pictures show Diana lying on her back on a piece of equipment designed to tone the thighs, and also seated with her legs spread while using a machine for the upper body. On the leg machine, the user presses the thighs against a metal plate to which weights are attached by a system of pulleys.

The photos were taken by a hidden camera, which was painstakingly installed in the ceiling above the leg press machine by Bryce Taylor, the health club's owner. "I know people will hate me for what I have done," Taylor told the Sunday Mirror. "But I'm not ashamed."

Nor is he poor. The Mirror papers paid him a reported $150,000 for British rights to the photos, and there were estimates that the sale of rights in other countries could easily make him a millionaire. Taylor cheerfully admitted that he had no intention other than to cash in on the fact that the Princess of Wales pumped iron in his club.

Buckingham Palace immediately issued a statement deploring the intrusion on the princess's privacy, and a spokesman said categorically that the photos were made without Diana's knowledge. The princess issued her own statement expressing distress at the incident.

Lord Oliver McGregor, who heads the voluntary Press Complaints Commission, blasted the Mirror papers and called for a boycott by advertisers. The Mirror responded by calling McGregor an "arch buffoon" and pulling out of the commission.

The Daily Mirror published more of the workout photos on Monday as Mirror editors sought to justify their decision. First they said it was a "security issue" illustrating how easy it would have been for a terrorist to get near the princess. Then they said the pictures were to dispel rumors that Diana was ailing and dispirited. Finally today, Daily Mirror editor David Banks admitted that taking the photos was "a particularly sneaky trick" but maintained that no editor on Fleet Street would have turned them down.

Monday night the princess won a temporary High Court injunction barring the Mirror from running any more of the pictures. This morning the princess sent her lawyers back to court seeking a permanent injunction against Taylor, the Mirror and anyone else who might have had a hand in the photos' dissemination. She asked the High Court to grant her possession of all the prints and negatives. She also asked for an accounting of any money Taylor or the newspapers have made from the pictures, indicating that she may seek to recover these funds as damages.

The tabloids generally consider the royals the easiest targets in town, since they almost never go to court. Sarah Ferguson, Prince Andrew's estranged wife, sued last year over topless pictures of her taken in the South of France, but that action was brought in the French courts, not in Britain.

More threatening, in the point of Britain's newspaper editors, are the rumblings from the government about tough new laws to curb press excesses.

"The fact that we are pursuing ... a tort for infringing privacy is clear evidence that there will be new laws," said Heritage Secretary Peter Brooke, whose department oversees the press.

Other newspapers -- perhaps with a touch of hypocrisy, given their own zest for scoops -- have been almost unanimous in condemning the Mirror. "The Mirror Group has jeopardized the integrity of the whole British newspaper industry with one stupid act," said the Evening Standard.

The princess's decision to file court papers may mean she has to appear in court. However, this is not guaranteed: She could be allowed to give written evidence, which would be read in court by her lawyers.