The row between the 85-year old billionaire Barclay brothers that exploded into the public gaze last week has moved up a gear, with Sir Frederick threatening to launch legal action against the family of his twin, David, if they try to sell the Ritz in London for less than £1bn.

The glitzy 114-year old property has a storied history, including hosting meetings between Winston Churchill, Dwight Eisenhower and Charles de Gaulle during the second world war. But now it has become the focal point in a 21st-century power struggle as dramatic as Succession, the hit TV series about a media empire run by a feuding family.

It was at the Ritz that the row erupted, when Frederick – who used the hotel’s conservatory for business meetings and to smoke his cigars – discovered he had been secretly recorded by his nephew Alastair. The culprit was caught on film handling the bugging device. Armed with that evidence, Frederick and his daughter Amanda, who works at the Ritz, dramatically thrust the family’s once famously secretive affairs into the spotlight last week by launching legal action in the high court.

The Barclay brothers’ business empire, built over 60 years, is ailing. Some of their main assets – the Telegraph Media Group, owner of the Daily Telegraph, online retailer the Very Group (previously known as Shop Direct and before that Littlewoods) and delivery firm Yodel – are under pressure and they have been considering sales.

The five-star Ritz is seen as a crown-jewel asset and is said to be closest to a sale. Reports have centred on the possibility it could be bought by a Saudi Arabian private investment firm for about £750m.

However, Frederick claims to have received at least two offers valuing the hotel, and associated properties William Kent House and Aldridge Street offices, in excess of £1bn.

In a rare public statement, Frederick, 85, the elder twin by 10 minutes, threatened legal action if a suitable price for the coveted property they bought for £75m in 1995 was not received.

“I take great pride in the Ritz hotel and its success ever since I personally wrote a £7.5m cheque as down payment in 1995,” he said. “There are 450 employees at the hotel who do a fantastic job.

“I can disclose that there have been a number of competing offers for this first-class hotel in excess of £1bn. I have no doubt that such offers will be considered, so that the Ritz is sold at the right time and for a proper price. There is no place for any sale at less than full value. A sale below the proper value would give rise to further litigation. This would be regrettable.”

Frederick and Amanda are threatening legal action over fears the business is being undervalued in a sale process they have no control over, as years of family infighting over the future direction of the empire and questions of inheritance come to a head.

Issues between the brothers have been building for years. Four years ago, a new headstone was placed on the grave of the once inseparable twins’ father, in Mortlake cemetery, west London. Only two of the six children put their names on the stone, David and his brother Andrew. Frederick’s name is absent.

The falling out between the twins, who used to live together on a mock-gothic castle they built on the private island of Brecqhou they acquired in the Channel Islands, now pits their respective families against each other.

At the same time Frederick and his wife, Hiroko, whom he married more than 40 years ago, started divorce proceedings in October.

Less than two weeks after David’s son Alistair was filmed red-handed with the bugging device, Amanda was removed from the company’s board. On the same day, two of David’s other sons, Aidan and Howard – who in effect now run the businesses – were appointed as directors at the Ritz.

In December, David strengthened his family’s grip on the empire, appointing Aidan and Howard as “persons with significant control” of Ellerman Holdings, the holding company for the Barclays’ UK assets. Each was given “more than 25% but not more than 50% of the share ownership and voting rights”.

The Barclay brothers are no longer beneficiaries of the family trust, and Amanda has been left with a 25% share, and no power to block David’s side of the family in any big decisions.

Desmond Browne QC, representing Frederick and Amanda in the bugging case, told a high court judge last week: “The children of Sir Frederick and Sir David have been at odds … cousin, sadly, has been pitched against cousin.”

As the family fight threatens the breakup of the twins’ media empire in the twilight of their business careers, Frederick hinted at the desire for some form of agreement.

“I am deeply shocked and saddened about recent events involving unethical conduct and intrusion into my privacy,” he said. “I hope we can get these family matters resolved so that we can all move on.”

But there is little sign that David’s family is quite so keen to move on. Their Ellerman company responded with its own statement: “Neither Sir Frederick nor Amanda Barclay have any relevant legal interest which would allow them to disrupt the sale process of the Ritz hotel, London,” it said, adding: “We remain focused on achieving the best value for all shareholders.”

Who’s who in the Barclay family

Sir Frederick Barclay

The elder of the twins by 10 minutes, 85-year-old Frederick is divorcing Hiroko, his Japanese-born wife of more than 40 years. She has hired high-profile lawyer Fiona Shackleton.

Amanda Barclay

The only child of Frederick and Hiroko, the 41-year old has worked at the Ritz. She set up the Frederick Hugh trust in her father’s name in 2014, which runs a school for special needs children.

Ko Asada Barclay

The 52-year old son of Hiroko and stepson of Frederick runs Koian, a property firm in London. He was one of the biggest donors to Ukip in the run-up to the Brexit referendum.

Sir David Barclay

Reportedly distinguishable from his elder brother only by the way he parts his hair (left; Frederick right), it is David’s family who has control of the twins’ empire.

Aidan Barclay

The eldest of David’s four sons, the 64-year old is the most well known, through roles such as chairman of Telegraph Media Group. His wife, known as Fizzy, is a well-known London socialite.

Howard Barclay

The 60-year old runs the family business alongside Aidan, holding a significant stake in the holding company for the Barclays’ UK assets.

Duncan Barclay

At 59, Duncan is the youngest son of Sir David’s first wife, Zoe. He is not part of the legal action bought by his uncle and is a trustee of Salvo, which heals anxiety and trauma through the word of God.

Alistair Barclay

The 30-year old is the youngest son of David by Reyna Oropeza, his Mexican-born current wife. Alistair, a former race car driver, was filmed handling the bug in the Ritz. He is involved with the loss-making online estate agent Yopa.