The firm of the corporate lawyer who will oversee the independent investigation in government contracts and lobbying was awarded more than £7m in government contracts over the past year alone, it can be revealed.

Slaughter and May, where the inquiry’s chair, Nigel Boardman, was a partner until 2019, has been awarded 10 contracts worth £7,229,989 since March 2020, according to analysis of government data, including by the Treasury and the Cabinet Office.

Boardman remains a senior consultant at the firm while he oversees the inquiry ordered by Boris Johnson following the Greensill lobbying scandal, after a number of controversies over the lobbying of cabinet ministers and officials by the former prime minister David Cameron and the connections of senior officials to the now-collapsed firm.

Slaughter and May has said Boardman is undertaking the inquiry in a personal capacity.

The analysis, which was conducted by the Labour party, found the law firm and its subsidiary, Slaughter and May Operations, had been hired by five different government departments to do legal work.

The contracts included urgent Covid-19 legal analysis for the Cabinet Office in June last year, billed at £950,000, and £3m-worth of legal advice to the Department for Transport.

The Guardian has previously reported that lawyers from the firm were “working as an integrated team with Treasury legal advisers” as the Treasury set up the Covid corporate financing facility (CCFF), announced by Rishi Sunak on 17 March 2020, according to a release on the firm’s website. That work cost £400,0000, according to the analysis of government contracts.

Rachel Reeves, the shadow chancellor of the Duchy of Lancaster, said: “Claims that the Boardman investigation is independent are lying in tatters. The more that emerges about this investigation, the more it looks like the Conservatives are set on glossing over cronyism in their ranks, so they can carry on like nothing has happened.

“We need to put a stop to this cycle of cronyism. That is why Labour is calling for a full, transparent parliamentary inquiry into the Greensill scandal.”

Labour has previously raised concerns about the firm’s connections with the regulation of ex-ministers’ business interests – one of the areas Boardman may examine in his review.

Sarah de Gay, Boardman’s senior colleague at Slaughter and May, and the firm’s special adviser on regulatory matters, has recently been appointed to the government’s advisory committee on business appointments.

That body advises former ministers and senior civil servants on whether and how they can take up appointments after their time in government, intended to prevent immoral use of former contacts but regularly criticised by transparency campaigners for being in effect toothless.

The Cabinet Office has previously defended Boardman’s appointment saying he was a distinguished legal expert who was “asked to lead this review following his own declaration of interests”. The review would examine “the facts thoroughly”, it said.

The Guardian has also previously reported that Slaughter and May made a joint submission with other law firms, approved by De Gay, that challenged the Cameron administration when the then prime minister proposed to change lobbying rules.

It suggested that adopting a blanket statutory register of lobbyists “may have the effect of stifling productive, even essential, dialogue”.

Boardman previously led a Cabinet Office review into the procurement process of Covid contracts early in the pandemic and is a non-executive director at the Department for Business, Energy and Industrial Strategy, a role he has said he will step back from during his time conducting the inquiry.

Three parliamentary inquiries have been launched since Johnson announced the Boardman review. Two of those, one by the Treasury select committee and one by the public administration and constitutional affairs committee, have said they will seek to call Cameron as well as the founder of Greensill, Lex Greensill, to give evidence.

Both Slaughter and May and the Cabinet Office have been approached for comment.