A campaigner against Lake District speedboat curbs has been found guilty of towing a 71-year-old blind water-ski champion too fast.

Tony Kemp, a Bingley accountant and member of Windermere Action Force, was caught on Coniston Water, magistrates heard.

The 44-year-old, of Lady Lane, represented himself and said the prosecution by the Lake District National Park Authority had been malicious and flawed.

Kemp has a holiday home in Windermere. He, his family and blind water-skier Gerald Price had been on Coniston to highlight a 10mph speed limit on nearby Windermere which comes into force next month. Later that day he attended a rally of more than 400 people protesting against the speed ban.

However, he denied he had gone to Coniston to break the law. He told the Court: "The case today is a malicious prosecution by the park authority. There is a complete absence of speed readings in the case. I have been accused of being a protester when the only thing I have done is have a fun day out with my family."

District Judge Gerald Chalk, sitting at Furness Magistrates' Court in Barrow, fined him £45 with £455 costs.

Water-skier Mr Price had told the court he was confident he was being towed at ten nautical mph during the outing. Kemp said the Coniston by-laws were unclear as they did not state whether the speed limit was in statutory or nautical miles per hour.

Ten nautical miles equals around 11.7 land-based miles, the court was told.

Kemp said the technique of "pacing" - park wardens in their own speed boat following Kemp to determine the speed of his blue and white Bayliner Capri boat - was unreliable.

The wardens used GPS, their own speedometer and a video camera. The prosecution said the technique was similar to that used by traffic police following a speeding car.

Kemp said the park authority was covertly filming him on the day. He claims the authority is reneging on a 30-year-old agreement to preserve Windermere for water sports by imposing 10 mph limits on Coniston, Ullswater and Derwent Water.

After the case, he said: "Three generations of our family have been using the Lake District for almost 40 years for watersports . My in-laws are in their seventies and still use a speedboat on Windermere.

"My wife and I have taken our three children to water-ski every year. It is absolutely awesome; its refreshing and invigorating. We water-ski during the day and then have a meal and chill out in the evening."

He said his conviction would lead to civil disobedience by lake-users. Many supporters attended the hearing. It follows protests to show a speed limit on Windermere would cut jobs, visitors and investors.