A PLEA has been made to the owners of a landmark Wye Valley country house to secure its future or make way for somebody who is prepared to do so.

A campaign to secure the future of Piercefield House, one of the UK's most important country houses, was launched with a picnic in front of the imposing ruin above Chepstow Racecourse.

The house, which has lain derelict since the end of the Second World War, is currently owned by the Reuben brothers, David and Simon whose wealth is estimated to be £8 billion since their acquisition of the racecourse.

London-based campaign group Save Britain's Heritage has made a public appeal to the brothers to protect what it calls "one of the most important country houses at risk in Britain today."

Supporters at the Piercefield picnic were urged to sign the open letter which tells the brothers: "This major example of British architecture cannot be allowed to collapse on your watch!"

Piercefield was designed by acclaimed architect Sir John Soane and was described by the botanist Joseph Banks – who sailed to Australia with Captain Cook – as the most beautiful place in the world.

Among the campaigners at the picnic last Friday was Sinclair Johnston who is structural advisor to the Church of England in Gloucestershire and has worked with several Forest churches.

He told supporters at the house: "It is like a grim experiment to see how long it will take for a great country house to fall into dilapidation."

Marcus Binney, the president of SAVE and an architectural historian, called for the Grade II* listed building to be sold or made weather-proof.

He described the efforts to secure the future of Piercefield as "the very frontier of preservation."

The letter to the Reuben brothers states: "SAVE Britain's Heritage has chosen to make it (Piercefield) the subject of a campaign.

"This major example of British architecture must not be lost to the nation. For this reason we have invited our friends, supporters and those with an interest in the house to join us at a gathering outside the house.

"You acquired the site when you became the owners of Northern Racing. At that time Piercefield House was on the market and you continued to allow offers to come forward.

"It is our understanding that a number of potential buyers came forward, but that you ignored their offers. In particular we know that an interested party in 2010, was ready, willing and able to restore it. He worked closely with an architect on a rescue plan for the building.

"However his offer was ignored. Unfortunately since then the buildings and land have been withdrawn from the market. Not only this, the main house has been separated from the land and parcelled off into an off-shore company.

"By separating the house from the land on which it stands you are alienating potential buyers and complicating the rescue of the house.

"Since you acquired ownership of the site seven years ago you have conducted some emergency stabilisation work to the house. These repairs are temporary holding measures: they are fast deteriorating and will soon need to be maintained, or replaced.

"Whilst effective in the short term the only real solution for the house is to find a sustainable solution.

"As a national charity that campaigns for the country's heritage we ask you – what are your future plans for Piercefield House? As the owners of a listed building you have a responsibility to either care for it or to allow someone else to do so."

It ends with a plea: "We take note of the extensive educational and philanthropic work of the Reuben Foundation and ask you to respond to this appeal from leading charities, trusts, bodies and individuals involved in the care of Britain's architectural heritage."

Nobody was available for comment from Reu­ben Brothers.