A Government backbencher has alleged that “gurriers” desecrated two national monuments in the Dublin and Wicklow hills.

Labour TD Eric Byrne criticised the “recklessness of scramblers, quad bikers and others engaging in antisocial activities”.

He claimed there had been an “amazing desecration” of a grave which had been recognised as a national monument. “People systematically tore the grave to bits.”

The Dublin South Central TD said the monument known as the Fairy Castle cairn had also been interfered with, and it seemed “people are trying to penetrate this particular cairn to see what may be beneath it”.

Mr Byrne said he had previously raised the issue when he spoke about “motorbikes literally riding right up on top of Seahan in and around “that most magnificent monument to those who lived in the area 5,000 years ago”.

He called for legislation to stop motorbikes, scramblers and quads “desecrating these very important landmarks in our mountain ranges”.

Minister of State Jimmy Deenihan, speaking for Minister for Heritage Heather Humphreys, said the hilltop cairn at Tibradden, Co Dublin, was a Bronze Age burial site dating from 1,800BC to 600BC. But the ground passage and chamber structure was actually a 19th-century feature. The cairn was in an isolated hilltop location and the protection of such monuments from interference “present challenges”.

The Minister was committed to using sanctions under the National Monuments Act but “she must also rely on the goodwill and vigilance of the public as one of the main ways to protect our archaeological heritage”.

The Department of Heritage was investigating the matter, and had brought it to the attention of the Garda.

Mr Deenihan added that the reported damaged “appears to be confined to the movement of loose stones from the cairn into the central chamber area”.