The sale of a leading UK mobile technology provider, owned by Roman Abramovich, has been halted by the government amid an investigation into the national security deal.

Officials at the Department for Business, Energy and Industrial Strategy (BEIS) have this week issued an interim order blocking the purchase of Truphone assets by Hakan Kok, a German billionaire entrepreneur, Sky News has learned.

The order, made under the new National Security and Investment Act, means the sale to Mr Cook cannot go ahead until a review is completed.

Kwasi Kwarteng, the business secretary, is understood to have signed the decision.

It was unclear this weekend on what basis the order was issued, although it is said to have been prompted by security services.

Truphone is a mobile virtual network operator in nine countries targeting international corporate clients such as investment banks.

Sources in the City said Truphone had entered into an embryonic remote SIM provisioning contract with BT Group, which they said could have raised concerns about the deal.

They added that Mr. Kok had said that he and fellow buyer Piros Kousias were prepared to exclude that contract from the purchase of Truphone’s assets.

The entrepreneurs’ deal with advisers Truphone is reported to be for £1, but is also understood to include a significant deferral based on the company’s performance.

The delay in the sale of Truphone’s assets comes at a difficult time for the loss-making company.

It is said to run out of cash in a matter of weeks, which could mean its directors have no choice but to put it into administration if a deal does not go through.

More than 400 people work for the company in the UK and abroad.

The process of selling Truphone has already been launched in recent months and Mr. Koc has been selected as the preferred bidder on an exclusive basis.

One of the sources said the temporary injunction resulted in a “vicious” outcome where Truphone effectively remained owned by a Russian oligarch who was already under sanctions.

Mr Abramovich and two Russian business partners are said to have invested more than £300m in Truphone during their time as shareholders.

The oligarch had already presided over the most high-profile sale of a British asset since Vladimir Putin’s invasion of Ukraine, in the form of the £2.5 billion sale of Chelsea Football Club.

Mr. Kok is a German-born businessman who co-founded the used car platform Auto1.

It listed on the Frankfurt stock exchange last year, and while its valuation has since fallen in line with publicly traded tech stocks around the world, it has crystallized Mr Kok’s status among the super-rich.

The government has come under pressure to demonstrate that the new national security laws are being implemented reliably, with Mr Kwarteng’s department last month saying they were working well – despite concerns raised by a number of leading City law firms.

“The Government is focused on growing our economy and equalizing every part of the UK, but this will not come at the expense of our national security,” he said.

“This report shows that our new investment screening process is working.

“It’s simple and fast, giving firms the speed and confidence to do business in a way that protects UK security.”

In total, more than 200 deals were notified to the government in the first three months after the law came into effect, with 17 deals registered by officials.

Mr Koch declined to comment on Saturday, while a government spokesman said: “While commercial transactions remain primarily a matter for the parties involved, the government regularly reviews purchases across the economy in the event of national security concerns.

“The business secretary has the authority under the National Security and Investment Act to intervene in acquisitions when appropriate.”

One city insider close to the proposed Truphone transaction said the decision to include it, with its potential risk to jobs, raised questions about whether the new law was being applied correctly.

“The government risks throwing the baby out with the bathwater,” the person said.

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