A historic King's Lynn building targetted by lead thieves is installing hi-tech security to try and keep the roof intact.

The 15th Century Red Mount chapel was hit for a second time last autumn when lead was stripped from the roof and damage caused to the guttering and brickwork. A similar theft took place a couple of years earlier and now new security measures are being introduced.

The Grade I listed building, also a scheduled ancient monument, was refurbished three years ago at a cost of �250,000 as part of a major regeneration scheme of The Walks which was backed by Lottery cash of �4.3 million.

Although the lead thefts have mostly been covered by insurance, West Norfolk council is determined to call a halt to the problem.

Both times the roof was stripped, some of the lead was recovered as it had been hidden nearby for collection later - but it could not be re-used on Red Mount because of the damage.

Scaffolding surrounding the prominent building is due to be removed in the next few days as the latest repairs have been completed.

But the new lead is covered in Smart Water - a security product which can't be seen but covers anyone who touches it in a flourescent dye which can only be detected under ultra-violet light. The dye cannot be washed off hands or clothing and contains a forensic code so police know exactly where it came from.

'It is a beautiful building and the thieves cause damage apart from taking the lead. It is such a shame and although we are insured, there is still an element of public money involved,' said Cllr Elizabeth Nockolds, portolio holder for sport, arts and open spaces.

'We have been talking to the police about the best way of protecting the lead and Smart Water is a good deterrant,' she added.

The council is also looking at installing sensors across the roof which will activate an alarm in the town's 24-hour CCTV monitoring station if anything is disturbed.

'If the sensors detect anything they will send a message straight through to the monitoring station where operators can call the police,' said Mrs Nockolds.

She added that it was impossible to have CCTV coverage around the whole building, although the main thoroughfares and play area in The Walks us completely covered.

The Red Mount was a wayside chapel for pilgrims on their way to the Shrine of Our Lady at Walsingham and is set on one of the highest points of the area.

The upper chapel, created in 1506, has a fan-vaulted roof and the building has also believed to have previously been used as a cistern, gunpowder store, stable and observatory. It was also a winter hibernation venue for both brown long-eared and natterer bats.

During the refurbishmet works two new roofs were created while the ceiling was cleaned and internal repairs carried out.

A tunnel through to the lower chapel was also reconstructed to allow access for people with disabilities.