It is the most expensive country-house sale in almost a decade. The Culham Court estate, an immaculate Oxfordshire pile on the banks of the River Thames, has been bought for just under £35m by one of Switzerland’s richest and most secretive financiers.

The 10-bed, Grade II*-listed property, which nestles in 650 acres of parkland, was snapped up by Urs Schwarzenbach, 57, who runs Interexchange, Switzerland’s largest private foreign-exchange company, and is said to be worth £880m (ranking him 60th on The Sunday Times Rich List). His clients include the Agnellis of Fiat and the Sultan of Brunei.

He had his offer accepted four days after the house went on the market in June at £25m, and exchanged contracts within a week, beating off fellow City heavyweights and some serious international interest. He and his wife, Francesca, a former Miss Australia, plan to move in later this year.

Clive Hopkins, head of farms and estates at Knight Frank, the selling agent, says of Culham Court: “It is a classic Georgian house in a perfect location. It doesn’t get any better than this.”

“We are thrilled at the thought of moving into Culham Court and making it our home,” the couple said in a statement. Schwarzenbach, a keen polo player and friend of Prince Charles, has lived in Britain since the 1980s, and will keep his current home at Shiplake, Thames-Side Court, for use by his family. It has been described as a “Disneyland-style park modelled on the train station at St Moritz”.

Schwarzenbach also owns a 26,000-acre Scottish estate, on which he has lavished more than £20m, reportedly adding a bowling alley, a marble-lined hot tub and a panic room in which to hide from potential kidnappers. There is also a £3m chalet in St Moritz, four other homes in Switzerland and 123,000 acres in Australia, including a ranch where Prince Harry spent part of his gap year.

The ties with royalty do not end there. Schwarzenbach is known to have invested £200,000 in Ardent, Prince Edward’s failed television production company, while Francesca is a godparent to Lady Louise, daughter of the Earl and Countess of Wessex.

The Swiss financier was also close friends with Kerry Packer, the late Australian tycoon, with whom he enjoyed an intense rivalry over the relative success of their personal polo teams.

Schwarzenbach spends about £500,000 a year on his own team, Black Bears, which he stables at the Guards Polo Club in Windsor. He also sponsors the rowing gallery of the River and Rowing Museum in Henley.

Neighbours will have to get used to the drone of his helicopter, the billionaire’s preferred mode of transport. Shiplake residents, including Raymond Baxter, former Tomorrow’s World presenter, objected in 1999 when he first flew in to the grounds of that estate. The publicity-shy tycoon commissioned a Mori poll to canvass local opinion, and later won the right to install a helipad.

The departing owners of Culham Court, Paddy and Annabel Nicoll, are remaining in the area. Annabel’s father, Martyn Arbib, former head of the Perpetual fund management company, bought the estate for her in 1997 for £12m, almost double the asking price, making headlines as one of the most expensive sales of the year.

Now it’s in a league of its own again. Hugo Thistlethwayte, a director of upmarket buying agency Prime Purchase, says: “A £30m house is rare. For a home with enough immediate land as an estate, I can’t think of a higher single sale in recent years.”

The speedy sale of the Culham Court estate is a sign of Britain’s buoyant top-end market. Knight Frank has sold 62 country houses with price tags of more than £4m this year, and in the same period Savills has sold 20 houses for more than £5m each. A third of them went to City buyers.

“A massive 70% of buyers’ wealth is City- or business-related,” says Crispin Holborow, head of the country department at Savills. “That confirms the importance of the financial community in the property market.”

Big country estate sales

£48m: Warter Priory estate, 11,000 acres in North Yorkshire, sold in 1998

£15m: Grade I-listed stately home Easton Neston, set in 550 Northamptonshire acres, sold in July 2005

£28m: Edgcote estate, 1,700 acres near Banbury in Oxfordshire, sold in October 2005

£24m: Sarsden estate, 600 acres in Oxfordshire, sold in February 2006

£30m: Clarendon Park estate, 4,000 acres near Salisbury, Wiltshire, sold in June 2006

£70m: Updown Court, a new-build mansion in Surrey with five swimming pools, is still looking for a buyer

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