Staff at an historic hall are having to invest in extra security after thousands of pounds worth of Yorkshire stone roofing slates were stolen.

The thieves struck twice in a week at Oakwell Hall in Birstall, which dates back to 1583. They stole roof stone from the visitor centre.

Senior museum officer Eric Brown said: "It will cost us thousands of pounds to replace each lot that's gone - it's the labour that costs more than anything - and it is becoming an increasing problem.

"We have already implemented extra security measures such as putting up bollards and other physical obstructions to vehicles and are looking at additional security for after-hours."

Yorkshire stone has become increasingly a target for thieves because of its value and rising cost and, according to Mr Brown, other places in Kirklees have been hit.

"We are having to restrict vehicle access to the car park at the visitor centre and regret the inconvenience this may cause," said Mr Brown.

"People can still park at the countryside information centre."

He said they had to step up security to protect the hall, its staff and visitors from further criminal activity. Oakwell Hall had suffered from sporadic incidents of Yorkshire stone theft, but it had become a major problem recently. He said the hall might install security patrols or cameras.

"The frequency of these incidents has increased as the demand and market value of the stone has increased," said Mr Brown.

A giant sculpture entitled Forlorn Hope, put up to mark the anniversary of the Battle of Adwalton Moor, was also vandalised. The giant poles representing soldiers' pikes were bent and damaged.

Councillor Brian Snelson (Con, Birstall & Birkenshaw) said the culprits were destroying Birstall's heritage.

"This seems to be an increasing trend," he said. "Birkenshaw Methodist Church has also been targeted. It has now taken all its Yorkshire stone slabs up and asphalted instead because they were being stolen. And Yorkshire stone has been stolen from the wall in Mill Lane in Birkenshaw, near the ambulance HQ.

"I don't see that Oakwell Hall has any choice other than to install more security. If they are causing so much damage, it's cheaper to install cameras than pay for repairs and labour each time."

A police spokesman confirmed they were investigating the theft of 50 Yorkshire stone roof slates, worth about £4,000, and appealed for anyone with information to ring (01924) 431059.