“Visitors do not observe social distances and set up tents and barbecues - and what they are using for toilet facilities does not bear thinking about!”

Sailors at Grafham Water are growing increasingly “disappointed and frustrated” that one of the UK’s top sailing venues remains closed because of the coronavirus.

They are upset that site owner Anglian Water shows no sign of slackening the lockdown on the use of the reservoir despite golf clubs and the countryside being opened up.

Anglian Water is to install large signs on the A1 and A14 warning that the reservoir is closed following large numbers of would-be visitors arriving and allegedly causing parking problems around Perry where they have been accused of breaking down barriers and being abusive to wardens.

Grafham Water Sailing Club (GWSC) member Jeromy Bosch accused Anglian Water of “corporate self-interest” at the expense of club members by keeping the reservoir - England’s third largest at nearly 2.5 square miles - closed.

Mr Bosch, a teacher who lives at Grafham, said: “Anglian Water is not currently prepared to permit the safe and socially distanced return to recreational sailing and windsurfing by members of Grafham Water Sailing Club despite the club having prepared a full risk assessment, including of water-based rescue activities and social distancing measures in line with Government guidelines.”

He said there had been no mention of refunds and that family membership cost him £500 but he could not sail.

Mr Bosch said: “Our club is a Royal Yachting Association-affiliated private members’ club with barrier-controlled access to the boat site. As members we closely follow any guidance given by our national association for all sailing-related sports and as sailors and windsurfer we are more aware of the need of keeping others and ourselves safe at all times and in any conditions. This is an integral part of or sport.”

He said he “fully supported” the initial lockdown at Grafham which was well-intentioned at the time, but the Government had since relaxed some of its rules about access to the countryside, including water sports.

Sheila Brighton, from Perry, welcomed Anglian Water’s decision to put up warning signs that the reservoir was closed following the arrival of large numbers of visitors.

“Sadly, the public will not accept this and each weekend Perry is flooded with visitors with nowhere to park or go,” she said. “No pub, toilets and cafe, a shop only open a few hours for papers, no cycling, fishing or walking.

“Rather than accept this, they park all around the village, often dangerously, and force entries into the ground by breaking barriers and they are often abusive the wardens who spend their days patrolling and moving them on.”

Cllr Brighton said Perry had a high proportion of very elderly residents who were afraid to go out at the weekends.

She added: “The visitors are often in groups and do not observe social distances and set up tents and barbecues - and what they are using for toilet facilities does not bear thinking about.”

A spokeswoman for Anglian Water would not comment specifically on the plight of the Grafham sailors. She said: “Our sites are currently closed to the public at this time. We know our leisure attractions are loved by many but protecting the health and safety of our colleagues and visitors is our top priority.

“Balancing the needs and wishes of all our active communities is always a challenge and we are all as keen as each other to get back to some sense of normality.

“However we must be certain that when we reopen we can do so safely, meeting all the guidance on social distancing. We are asking everyone to please respect the difficult decision we have made at this time.”

The spokeswoman said: “Protecting our staff has been at the forefront of our minds since the lockdown began, even though hundreds are out working every day to keep essential services flowing. We don’t want our colleagues to face abuse as has sadly been the case recently. It’s also very important to us to make sure our park staff are not being expected to police visitors or manage social distancing with crowds either.”