NATIONAL park officers have vowed to continue a campaign against illegal off-road drivers and motorcyclists.

Staff at the North York Moors National Park Authority have held a number of action days with police in a bid to combat the problem.

At the most recent event in February, two warning notices were issued and five juveniles were found illegally riding quad bikes in Harwood Dale Forest.

Responsible trail riders are calling for some way of putting up signposts for the routes they can legally use.

North Yorkshire Police have also been writing to registered keepers of vehicles found to have brought motorbikes into the area to further encourage responsible riding.

Karl Gerhardsen, access and recreation officer for the authority, said: "Quad bike usage is increasing and the last action day was the first to encounter a micro trail bike.

"Predictions suggest that the demand for off-road motorcycling and driving continues to increase.

"The reality is therefore an increasing demand for legal routes to be better defined and maintained and for more sites that can provide for recreational off-road motor sport."

The Natural Environment and Rural Communities Bill currently before Parliament could make it easier for English Nature to prosecute people causing reckless damage to fragile habitats or protected species.

There will be a potential fine of £20,000 for offenders.

Mr Gerhardsen is planning to work with English Nature, the police and the Crown Prosecution Service to draw up a checklist of essential factors needed for such a prosecution when the bill becomes law.