Off-road motorcyclists and fly- tippers are destroying a historic Anglo-Saxon earthwork near Keynsham, heritage experts said yesterday. Now Avon and Somerset police have teamed up with English Heritage to protect the site and other ancient monuments in west Wansdyke.

Archaeologists believe the earthwork, just outside Compton Dando, dates back to either early Anglo-Saxon or late Roman times.

Susan Smith, assistant inspector of ancient monuments for the south west branch of English Heritage, said they were anxious to bring those damaging the site to book.

She said: "The aim of the initiative is for us to build a closer relationship with the police.

"We can then reduce the number of incidents of damage to scheduled monuments and, where necessary, secure convictions against those responsible for the damage.

"It is important that English Heritage inspectors are involved at the first possible opportunity as the statutory guardians of these monuments.

"We have the expert knowledge to evaluate the damage, and by working closely with the police we hope to achieve our aims."

Besides west Wansdyke, English Heritage and the police are also cracking down on vandals at Brean Down in the Bristol Channel and Cheddar show caves.

All three sites are protected by the 1979 Ancient Monuments and Archaeological Areas Act, which makes damage to the sites illegal.

Pc Dave Cooper, crime reduction officer at Avon and Somerset Police, said the force was working with English Heritage to cut vandalism.

He said: "It is vital that we work together to safeguard these hugely important heritage sites so that they can be preserved for future generations to enjoy and learn from."

The campaign also has the support of the National Trust.

Martin Papworth, the trust's regional archaeologist for Wessex, said: "The trust welcomes this initiative and hopes that this joint approach will lead to greater protection of our heritage sites."

t.bradshaw@bathchron.co.uk