STAFF at the National Gallery were threatened with arrest and the Official Secrets Act after media leaks that an unauthorised portrait of Brian Cowen had temporarily hung in the museum.

The bizarre threat was made at a staff meeting on Thursday morning when workers were told they could face serious repercussions if any more information is leaked to the media.

It is understood a second garda investigation has now begun into how the Sunday Tribune first found out about the hanging of the picture in the Portraits Gallery by painter Conor Casby.

However, a spokeswoman for the National Gallery would not confirm whether they had followed up on a threat to make a formal complaint about the purported "media leaks". A statement said: "The National Gallery does not make specific comments on security issues for obvious reasons. However, they continue to be under constant review."

When quizzed further about whether they had requested a second investigation by gardaí into the matter, they said: "As a matter of policy, the National Gallery of Ireland cannot comment publicly on matters relating to security issues."

However, staff were called to a meeting with embarrassed gallery management on Thursday morning and warned that leaking information was a criminal offence.

One worker said: "The staff were warned they would be open to arrest under the Official Secrets Act and the Data Protection Act if they released information to reporters or the general public.

"From what we can gather, the Department of the Taoiseach was none too happy with what happened and what they perceived as the lax security that led to the incident in the first place.

"As far as the workers are concerned, there is a major shortage of manpower in the National Gallery and that was directly responsible for any breakdown in security."

The Sunday Tribune has also learnt that another two breaches of security have taken place since the Cowen painting was hung almost a month ago on 7 March.

Eight days ago, a poster advertising an exhibition featuring nude portraits of Taoiseach Brian Cowen was hung in the Merrion Street lobby of the National Gallery. It was quickly removed by security staff.

On Monday, the pranksters were back and left leaflets featuring reproductions of the notorious Cowen painting with the caption "censor this" written across them.

The offending items were again removed and the gardaí were informed.

A National Gallery source said: "As far as the police are concerned, it was another case of guerrilla art. They aren't getting too excited about it because they are chastened by what happened the last time they got involved.

"The suspicion is that it is art students who are responsible for the two latest incidents. The gallery has become an obvious target now, so security is on high alert."