Convicted armed robber Mark Kenny was wrongly let out of the prison on 20 June after his namesake, who was serving a sentence for road traffic offences, was granted temporary release.

The 30-year-old from Ballyfermot was not due to be freed until 2010 but took full advantage of his good fortune and managed to go home and get his passport before gardai were alerted.

Over the last two weeks, five postcards meant for Kenny's former prison friends have been intercepted by staff at the jail.

The postcards have been sent from mainland Spain, Lanzarote and Tenerife and boast about how much the criminal is enjoying being a free man in the sun.

They have been handed over to gardai to investigate but sources say there is little chance Kenny will be caught and returned to Ireland.

Dozens of Irish criminals operate from Spain and the Spanish islands, and the region around Alicante is nicknamed the Costa del Crime.

A source said: "Every letter that is sent to a prisoner in medium- and high-security jails in Ireland is read and censored by staff. When the first postcard arrived to a prisoner who was a good friend of Kenny's, the alarm bells immediately went off.

"He was purely acting the maggot talking about life on the beach in the sun. He knew that it would never get through and was just taunting us over the mistake in letting him out.

"The gardai will now be investigating, but in reality there is very little hope that he will ever be found and we will just have to ensure that something like this never happens again."

Kenny was serving a sixyear sentence and is described as dangerous. The Mark Kenny who was supposed to be set free was serving a threemonth sentence for traffic offences.

The prison service says there were remarkable similarities between both men.

They looked alike in their prison photos and signed their names in the same way. Both also had similar tattoos on their bodies.

Brian Purcell, the head of the prison service, ordered an immediate inquiry.