Jian Jun Xi, 37, and Yuan Cai, 43, said they were "visual artists" attempting to make Tracey Emin's work more interesting.

The BBC's John Kay: Fears that performance artists would carry out an attack of this sort

Her creation, My Bed, is one of the most contentious pieces of art on this year's Turner Prize shortlist, featuring an unmade bed with grubby sheets, surrounded by condoms, soiled knickers and bottles of vodka.

It is one of five works of art shortlisted for the £20,000 prize - and which art-lovers have been flocking to see at the Tate.

Kung fu artist

The artists said their action was an art work in itself, which they had named Two Naked Men Jump Into Tracey's Bed.

Mr Xi, divorced, from Camden Town, north London and a British citizen originally from China, said: "We wanted to push her work to further limits, make it more sensational, interesting and significant.

"We're trying to challenge these artists."

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Mr Xi, who studied art at Goldsmiths College, London, added: "We went in and took our clothes off very quickly.

"We had slogans on our body in Chinese and English and jumped around for about 15 minutes before the security guards got hold of us.

"People seemed to enjoy it, then three security guards got on top of me and I was bleeding. They were very ignorant."

Mr Cai, of Stoke Newington, north London, whose son was at the performance, said: "Tracey's work was strong but it wasn't strong enough. We wanted to push the idea further.

"Our action will make the public think about what is good art.

"We had 'isms' all over our bodies. Like idealism, internationalism, anti-stuckism all relating to our work."

Calvin Kelin stunt

Mr Cai, a married graduate of the Royal College of Art, said: "I was going to pull off my Calvin Klein pants and put Tracey's knickers on, but I didn't have time to do a proper performance.

"I tried to scare the guards by pretending to be a kung fu artist."

The artists said they had been detained for four hours and claimed Ms Emin and the Tate Gallery had not minded about their actions.

Scotland Yard said the men were released without charge. It is understood the gallery decided it did not want to press charges.

A spokeswoman for the Tate said: "The work has now been restored and the exhibition will open to the public as usual."