The prankster who created a furore when his nude portraits of Brian Cowen, the Irish Prime Minister, were hung in two of Dublin's most prestigious galleries faced prison yesterday after police discovered his identity.

Conor Casby, 35, a shy, Dublin secondary school teacher, has been credited with Biffo on the Bog and another unflattering - and uncommissioned - portrait of the Taoiseach. Police have interviewed the guerrilla artist and are preparing a file for the Director of Public Prosecutions.

Mr Casby could be prosecuted for indecency, incitement to hatred and criminal damage - for hammering a nail into a wall of the National Gallery of Ireland. If convicted, he would face a heavy fine and possibly even a stint in jail.

Also in the dock is RTÉ, Ireland's leading public broadcaster, for daring to report the incident. After receiving a formal complaint from the Taoiseach's office, the Irish equivalent of the BBC was forced to issue a grovelling apology to Mr Cowen on its main evening bulletin.

The offending artworks set out to mock Mr Cowen, better known by his nickname Biffo, which stands for “Big Ignorant F***er from Offaly”.

One, which was smuggled into the National Gallery, pictured the Irish leader on the toilet holding a toilet roll. It remained on display for 20 minutes before security took it down.

The other painting, portraying the Taoiseach holding a pair of blue and white Y-fronts, was hung in the Royal Hibernian Academy.

The success of the stunt seemed to provide a welcome respite from the barrage of gloomy economic news, but the authorities took a different view.

Will Hanafin, a producer at the Dublin radio station Today FM, said that Mr Casby had contacted him on Monday to confirm that he was the artist. He described the artist as “a very nice, meek and humble man who is freaked out by the reaction” to his creative endeavours.

The two men had been in correspondence previously by e-mail. He said that while Mr Casby confirmed he was the artist he denied that he was responsible for hanging the paintings in the public galleries.

Mr Hanafin said that once the artist's identity was revealed by the radio station the police arrived. A detective told him that he was under “pressure from on high ... the powers that be wanted it investigated”.

When Mr Hanafin refused to hand over the artist's e-mail details to the officers he said he was warned that police would seek a search warrant for the station's premises in order to obtain the information.

Mr Casby later accompanied police officers voluntarily to a Garda station to be interviewed about the incidents in the galleries.

RTÉ, meanwhile, removed its light-hearted story from its website and delivered a contrite and sombre apology, read by one of the nation's best-known news presenters.

The state broadcaster apologised for any personal offence caused to Mr Cowen or his family and for any disrespect shown to the office of the Taoiseach.

That was in stark contrast to the jovial tone of the offending news story of the night before, in which the newscaster said with a straight face that the Taoiseach was “not thought to have posed for the anonymous artist”.

The apology prompted fevered discussion on blog sites, with much criticism of RTÉ and the Garda Síochána - the police - as well as caption competitions for the offending paintings. Michael Kennedy, a member of the Irish Parliament for Fianna Fáil, the ruling party, which Mr Cowen leads, insisted that the RTÉ report was “a gross insult to the dignity of the office of Taoiseach”. He called on RTÉ's director-general to tender his resignation.

However, Fine Gael, the main opposition party, said last night that the affair was “more reminiscent of Russia in the 1930s than Ireland in 2009”.

The party called it a “scandalous waste of resources” for detectives to be investigating “what amounted to a practical joke that offended the Taoiseach's ego”.

“Today FM has clearly come under pressure to hand over e-mails about this matter while RTÉ News was obviously browbeaten into a grovelling apology,” Charlie Flanagan, a spokesman, said.

“The Taoiseach's overreaction to what amounted to satire is completely over the top.”

As for the amateur and now infamous artist, Mr Casby said in a statement that he “would like to draw an end to this by offering the portraits to the highest bidder and donate the proceeds to charity”.

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