Off-roaders have turned an area protected because of its special scientific value into a "mud bath".

A beautiful area of Ranmore Common, which has been designated a site of special scientific interest by Natural England, has been badly damaged by off-road vehicles.

Andy Goodwin, National Trust warden for Ranmore Common and Polesden Lacey, said: "They have turned it into a mud bath.

"There is a lot of deadwood there, which means there are lots of wildlife and invertebrates living there.

"It is one of the few areas that has been left the way it is and they have destroyed it.

"For the last three or four years, we have had problems, but a lot of the damage has been in the last six months.

"We closed off one way in but they found another way in and have been racing around.

"Every time we try and improve the area they get back in.

"I don't really think it is 4x4s.

"I think it is little Suzukis and bikes.

"They have trashed the area.

"Anything that was living in the long grass will be long gone."

A spokesman from Natural England explained why the area is so important.

He said: "Some of the woodland (notably Bagden Wood and Dorking Wood) is ancient, while the remainder has developed over former heathland or rough pasture, some of which survives in the more open areas.

"The site supports a diverse community of breeding birds including sparrowhawk, woodcock, tree-pipit, redstart and hawfinch.

"Damage to the forest floor can disrupt the ecological processes of the forest.

"At this time of year, the ground can easily be churned up, breaking emerging bluebell shoots.

"This can spoil the spectacular blue carpet in the spring and take away a vital resource for the forest's wildlife."

Malcolm Johnson is councillor for the Ranmore area and also lives nearby.

He was saddened to hear of the damage.

He said: "The area is well used by walkers, cyclists and horse riders, and I hope I will be able to work with the National Trust to stop this happening again."

Surrey Police said it also takes a tough stance on illegal off-roading.

John Tadman, Mole Valley neighbourhood inspector said: "If we find vehicles off-roading in areas they should not be, they face prosecution under Section 59 of the Police Reform Act.

"Whereby we can seize the offending vehicle and the owner will have to pay to get them back and can face court for the offence."