Labour has raised concerns about the appointment of Whitehall business roles currently at the centre of the Greensill lobbying scandal after it emerged one is held by a major Conservative donor.

Daniel Green, an entrepreneur who gave around £135,000 to the Tories in the run-up to the 2017 general election, was made a crown representative while David Cameron was still prime minister. The same position allowed Lex Greensill controversial access to major government departments.

That revelation has led to growing questions over whether the system of crown representatives – business people brought into the heart of Whitehall to help secure value for taxpayers’ money – is fit for purpose.

Shadow Cabinet Office minister Rachel Reeves told The Independent that the case “raises concerning questions about the links between Tory donors and crown representatives. Given growing concerns about revolving doors in government, we need urgent reassurances that stronger checks and measures will be put in place to tackle the Tory sleaze scandal.”

Boris Johnson has ordered an official investigation into the Greensill lobbying scandal, which erupted after it emerged that David Cameron texted the chancellor Rishi Sunak to urge him to include the company in a government Covid recovery scheme.

On Friday it emerged that financier Lex Greensill was announced as a crown representative by the same senior official he later employed at his firm, Bill Crothers.

Whitehall sources expressed shock last week when it came to light that Mr Crothers later started a job with Greensill while still working as a civil servant, a combination he insisted was not unusual.

Another crown representative, David Brierwood, also combined the Cabinet Office role with being a director at Greensill, for three and a half years.

The government-ordered inquiry has faced accusations that the prime minister is trying to mark his own homework.

In response, the National Audit Office and a number of parliamentary committees have announced they also intend to carry out their own inquiries.

Mr Green, who is the crown representative for the energy sector, said he did not accept any salary for the role and estimated that he had saved the taxpayer millions.

He said: “I agreed to become a crown representative on the basis that I wouldn’t claim any reward including the salary which comes with the role or any expenses. It was my way of giving back to this fabulous country. As a Jewish person you will understand that I feel very privileged to be able to continue my faith and contribute to this society without prejudice. I look forward to my children doing the same.

“Unlike the other crown representatives I have a slightly different role which is more akin to general business advice and I do not have direct contact with any of the strategic suppliers of the government. Therefore there is no conflict nor do I believe that there could be one within my remit.

“With regard to my donations to political parties, it is true that I have made donations to both major parties. The Labour donation was with regard to a candidate for London mayor some years ago. My Tory donations were in respect of the opposition being Ed Miliband and Jeremy Corbyn.

“In both cases particularly the latter I was concerned that life as a Jewish person may become more difficult in the United Kingdom.

“I have not donated since as I actually feel that the current opposition is healthy. I also feel that their stance on green issues which are close to my heart could be more genuine and deliverable and I include Ed Miliband in that summation.”

He added: “I’m proud of the work I have done at my own expense. I believe real long term satisfaction comes from giving.”

Downing Street said crown representatives were recruited for their working knowledge of specific sectors to communicate government needs and identify areas for cost savings, to save money for the taxpayer.

A No 10 spokesman added that they have no role in and do not participate in the procurement process.

A Cabinet Office spokesman said: “Crown representatives do not participate in the procurement process nor are they able to award any contracts. They are part-time senior executives recruited for their working knowledge of a sector to help ensure value for money for the taxpayer.

“All crown representatives go through regular propriety checks and cannot work with a supplier where there could be a conflict of interest.”