REPAIRS to damage caused by treasure hunters at Silbury Hill are planned - 227 years after their dig.

Three years ago, a gaping hole appeared at the top of the manmade hill, which archaeologists say was constructed at least 4,500 years ago.

Work by English Heritage in 2001 prevented further collapse and now the same organisation is planning work to repair the damage once and for all.

Meanwhile the 130ft hill whose purpose remains a mystery in spite of centuries of investigation is to be featured in a Channel 5 television documentary about England's finest ancient monuments.

Sited near Marlborough and part of the World Heritage site, which also includes Avebury and its standing stones, the hill will feature alongside attractions such as Dorset's Cerne Abbas Giant and Tintagel Castle in Cornwall.

English Heritage spokeswoman Catherine Edey said: "In 2001, English Heritage carried out work to arrest a collapse to the head of a shaft which, in 1776, had been sunk by the Duke of Northumberland to the centre of the hill.

"Following this work, a geophysical survey of the whole hill was carried out on our behalf by Skanska Cementation.

"Reassuringly, they reported that the hill was a robust structure which was basically stable.

"But they identified certain areas which required further investigation."

She added that more investigations had been carried out below a blemish to the northern flank of the five-and-a-half acre mound but no problems were found.

The current work involves investigating the previously-collapsed shaft, including the consistency of previous generations of backfilling of the 1776 dig.

That shaft was dug on the Duke's behalf by miners, after the aristocrat became convinced treasure was buried there.

The new work involves the digging of boreholes and extraction of soil samples from the base of the old shaft.

Ms Edey added: "The information gathered will help us design long-term remedial work."