Vandals have scarred an ancient settlement with graffiti.

Police in Orkney are looking for those responsible for defacing the neolithic village of Skara Brae above Bay of Skaill on Orkney's west coast.

The culprits may have left an important clue in their daubings. They wrote: "Brian Finlay slept here 13-8-2007" and "scouse celts". Police say that this suggests the damage may have been caused by visitors who spent the night at the 5000-year-old site.

Skara Brae is seen as one of the archaeological treasures of the world, attracting thousands of visitors every year. Radiocarbon dating in the early 1970s showed the settlement was inhabited between 3200 BC and 2200 BC.

On Tuesday, Historic Scotland staff found the graffiti in house one in the settlement.

A spokeswoman said yesterday: "Historic Scotland is both saddened and disappointed that such an act has occurred, as I am sure is the local community. Our visitors have reacted with surprise and sympathy to the damage caused. We have around 650 visitors a day to Skara Brae at this time of year who travel there from all over the world. Skara Brae is a hugely significant site. It is one of Scotland's national treasures and forms part of a World Heritage Site."

A specialist team at Historic Scotland's conservation centre in Edinburgh are looking at the most appropriate method of removing the graffiti at the earliest possible opportunity.

A CID spokesman in Orkney said police were looking for the six occupants of a Silver Hyundai Matrix, registration number LT56 CZJ.

Skara Brae was discovered in a winter storm in 1850. Gale force winds and extremely high tides stripped the grass from the mound known as Skerrabra. This partially revealed the outline of some of the stone buildings.