Legendary upmarket estate agency Beauchamp Estates has marked its 40th year in business by announcing expansion plans.

Beauchamp Estates was founded in 1979 in central London by Gary Hersham and has been behind some of the biggest and most prestigious residential property deals in the world.

At a retrospective art and property exhibition held in Mayfair to commemorate the anniversary, 40 of the biggest trophy deals were showcased – worth a combined £3.4bn in today’s values.

The agency’s first deal four decades ago was an apartment in Mayfair which sold for a mere £120,000, while last year it sold a mansion in Belgravia Square which had been the London home of the Dukes of Westminster for £50m.

Last year, it also sold a country home in Washington DC for £53.4m, a record for the area. The house had once been owned by the Kennedy family.

The firm also set a record in 1998 when it sold a large house in central London for £2m in under four hours.

Recently this year, it has let a mews house in central London for 12 months at £1.04m in one of the biggest rental deals ever done in the UK.

The firm is currently selling property in London and the home counties, France, Greece, Italy, Israel and the US.

Hersham, who appeared on the BBC ‘spy on the wall’ documentary series Under Offer back in 2014, said: “We are delighted to be celebrating 40 years of success.

“I  am extremely proud of the Beauchamp Estates team and everything the business has achieved.

“The market-making deals achieved are a testament to the team’s dedication. We have exciting expansion plans for the future, in both London and overseas markets.”