Meg Hillier, chair of the Commons public accounts committee, is also planning to grill civil servants from the department when they appear before her committee later this month.

"The size of a company or its connections should not have any bearing on whether HMRC go in and do an investigation," she said. "I think they should explain to the British taxpayer what their rationale was for refusing the request."

Meanwhile shadow chancellor John McDonnell said the Conservative party had "serious questions to answer".

"If true, these are deeply concerning revelations," he said. "The fact that a Tory donor could be allowed to potentially subvert the system will look bad to taxpayers who play by the rules.

"The Tories have serious questions to answer on this matter, and I hope the chancellor immediately comes forward to explain this behaviour by HMRC and ensure there was no undue pressure exerted by Conservative party politicians or officials."

Labour leader Jeremy Corbyn said: "HMRC is a government agency, it is part of our government, and it should investigate every company without fear and without favour about its tax affairs to make sure they pay the correct amount of tax and there's no hiding place, no evasion from it, whoever they are."

Number 10 attempted to play down the row, insisting that the line on being a Conservative donor was only included in official correspondence "as background".

"My understanding from HMRC is that the information was only provided as background to offer a detailed profile of the company to their French counterparts, but it was not taken into account by HMRC in deciding whether to support the French application," the prime minister's spokesperson said.

"HMRC never takes political donations into account when it makes decisions on whether to investigate a business. The request was rejected because it did not contain sufficient information for HMRC to seek a search warrant.

"We're absolutely clear that we take a zero-tolerance approach to corruption."

Prime minister Theresa May has vowed to "act vigorously" against those suspected of money laundering, to "safeguard the integrity of Britain’s financial economy".

Yet since BuzzFeed News revealed that Lycamobile was depositing rucksacks stuffed with hundreds of thousands of pounds of cash at Post Offices all around London — practices experts said should raise red flags with anti-money laundering and tax authorities — the government has taken no criminal action against the company, even after the French launched their money laundering probe.

Meanwhile, the Conservative party has accepted a total of £2.2 million from Lycamobile — including more than £800,000 after BuzzFeed News first exposed the company’s suspicious business practices.

In a statement this week, the Conservatives said they had decided two years ago to stop taking any further money from Lycamobile. The party last accepted a donation from the telecoms company in late July 2016, a month after BuzzFeed News revealed the French money laundering raids.