Manx National Heritage says it is ‘extremely disappointed’ after fire damage was caused to an Iron Age hill fort for a second time.

The latest incident took place last week at the Cronk ny Merriu promontory fort which is located off the Raad ny Foillan coastal footpath at Port Grenaugh.

Revellers had lit a campfire and left the cliffside grass platform smouldering and the site littered with broken glass bottles and other debris.

MNH said this was the second time that damage had been caused to the site - and on the previous occasion the emergency services had to be called as a fire from a disposable barbecue spread to the cliff.

The ancient monument, complete with defensive ditches and rampart, is thought to date back to the first centuries AD although there are also foundations within of a 10th century Viking longhouse.

Tony Cain, a part-time lecturer in Manx history and archaeology at University College Isle of Man, discovered the damage when he was leading a field trip with a party that included visitors from Oregon, USA.

He said: ‘The interior grassy platform of the fort was strewn with debris including broken glass bottles, plastic bottles and the interior drum of a washing machine which had evidently been used to light a fire.

‘The remains of the fire littered the platform and the grass at the south facing cliff edge was still smouldering.

‘Such behaviour shows a wanton disregard for both a site of national importance and the island's magnificent coastline.

‘It is not the first time that I have visited this site and found a campfire had been lit. One despairs at how low some people can stoop.’

Cronk ny Merriu translates as ‘Hill of the Dead’ and historians had originally assumed it was a prehistoric burial mound.

But excavations revealed a fortified headland complete with a rampart.

A spokesperson for MNH said: ‘Manx National Heritage is extremely disappointed by recent littering and fire damage at Cronk ny Merriu.

‘We are very grateful to the member of the public who reported this and to those who stepped in to clear away the mess left behind. 

‘A previous episode involving a disposable barbecue resulted in a fire spreading to the cliff which was only extinguished with the help of the emergency services. 

‘Fortunately, the fire did not spread to the headland this time, although the scars will be visible at Cronk ny Merriu for some time to come.

‘It is against the law to damage ancient monuments, which are legally protected forever, for the benefit of the public.  Fire is a particular risk as it directly affects the archaeological remains that are present below the surface.’