Then it checked the historical records. But nowhere could it find any reference to 'Fr Pat Noise', a mysterious figure who has recently been commemorated on the capital's main thoroughfare.

Council officials are now investigating the possibility that they have fallen victim to pranksters who have placed a commemorative plaque to a 'Fr Pat Noise' on O'Connell Bridge. The bronze plaque, which claims to mark the priest's death in 1919, can be seen on the wall at the bridge, but council officials this weekend said they have never heard of the plaque . . . or of Fr Noise.

The council is now probing how the unauthorised plaque ended up on Dublin's landmark bridge, with officials suspecting that the plaque, which measures six by eight inches, was placed there as a hoax. A spokeswoman for the council said it was "completely unaware" of any memorial on O'Connell Bridge to a Fr Pat Noise.

The plaque, which even contains a picture alleging to be that of the mysterious religious figure, claims to mark the spot on which Fr Noise died "under suspicious circumstances when his carriage plunged into the Liffey on August 10th, 1919." The plaque states that Fr Noise was an "adviser to Peader Clancey."

After being informed by the Sunday Tribune of the plaque's existence, council officials inspected it on Friday afternoon and hope to identify when and how it was placed into a hole on top of the wall on the bridge. The plaque is located on the Ha'penny Bridge side of O'Connell Bridge, near to the traffic lights on Bachelor's Walk.

The plaque claims to have been erected by an organisation called "the HSTI", although the heritage department of the city council said it had never heard of a group by this name.

"Council officials had a look at the plaque [on Friday] but they said they had never seen it before, " said a spokeswoman. "It is certainly very unusual for this to happen."

The council said that it was possible the plaque was erected legitimately a number of years ago, although this would seem most unlikely given that nobody seems to have noticed it until last week.

The rough manner in which the plaque is inserted into the wall would also suggest that it was placed only recently. Although it appears expertly made, it is too small for the hole, which has several rough edges.

Council officials will now attempt to pinpoint the age of the plaque and the historical significance of 'Fr Pat Noise' before making a decision on whether or not to remove the memorial.