The president of Kazakhstan has secretly bought one of Britain’s most expensive homes, according to the former head of his country’s security service.

Toprak Mansion in The Bishops Avenue in Hampstead, north London – known as Billionaires’ Row – was bought for £50m by a company controlled by a property tycoon.

The former Kazakh intelligence chief said the company was acting as a front for President Nursultan Nazarbayev.

“Toprak Mansion is owned by Nazarbayev,” said Alnur Musayev, who used to run the successor to the Soviet-era KGB in the central Asian state. The president, he added, wanted to disguise his part in the transaction.

Hossein Ghandehari, who bought the house with his Kazakh-born mother, Hourieh Peramam, 75, denied the claim.

Ghandehari did say, however, that he knew the president and worked with his family on “charitable and philanthropic” projects. Ghandehari, 43, said: “We know Nazarbayev’s family quite well [but] we haven’t done any dealings with them.”

The Ghandehari/Peramams are said to have accumulated a fortune of £1 billion through buying property in Britain and abroad.

However, the high price paid for the gaudy neo-classical villa and the identity of its buyers surprised many in the property world, who had never heard of them.

Musayev’s claim raises questions over the origins of much of the money from the former Soviet Union that has flooded into the British property market.

Toprak – nicknamed Top Whack when it was bought in January – is the most expensive of a string of properties the Ghandehari family has bought in The Bishops Avenue since 2002.

Musayev said the purchase was part of Nazarbayev’s policy of placing his money abroad.

He claimed that the Kazakh president had personally profited from the wealth of his oil and gas-rich country. “There has been a trend to invest in property and land in Britain,” said Musayev, who is also the former head of the president’s personal bodyguard and was forced into exile in Austria last year when he was accused of taking part in a plot to over throw Nazarbayev.

Intriguing details of Ghandehari’s business background have also emerged.

A former worker at a London branch of Burger King has claimed that Ghandehari offered him money to open a bank account ready to channel a sum of $1m (£640,000) into Britain.

Ehsan Mirafzal said he was a manager at an outlet of the fast-food chain in Tottenham Hale, north London, when a mutual friend introduced him to Ghandehari.

He said Ghandehari asked him to help to launch a limited company, Lenard Ltd, which was incorporated in 1999, as well as to open the account.

Mirafzal acted as company secretary and was a director of Lenard alongside Ghandehari and his wife, Yassmin.

Ghandehari gave an address in Tehran.

Mirafzal, who opened a Lloyds TSB bank account in the company name, said he thought the money was intended to pay for a consignment of metal from a foreign country, possibly Russia, which would probably go to Iran. In return, he said, he was promised a commission of 5% – about £32,000.

“To be honest with you I don’t know what it was [the commodity or what the money was for] but I just thought ‘he’s been introduced as a friend’ and he says, you know ‘just have something’.”

Mirafzal said that when the transaction did not take place he became disgruntled and closed the bank account.

He said: “Money just coming into my account . . . and going out just like that – maybe it’s not supposed to happen.”

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