Senior Labour MP Harriet Harman has demanded to know the government's involvement in the failed prosecution of human rights firm Leigh Day.

In an open letter to attorney general Jeremy Wright published today, Harman said pressure exerted on the Solicitors Regulation Authority to bring proceedings 'undermined the rule of law', and was designed to deter solicitors from taking action against the government.

Leigh Day, which ran claims for Iraqi civilians against the Ministry of Defence, was cleared of wrongdoing by the Solicitors Disciplinary Tribunal last month following the longest hearing in its history. The costs are set to rise above £10m and will be subject to a further hearing later this year.

Harman, who started her legal career as a solicitor at Brent Law Centre and was later solicitor general in the Blair administration, demanded to know the content of emails sent from government departments to the SRA in the build-up to the prosecution, and whether Wright knew about them.

She asked whether Wright agreed such emails were 'wholly inappropriate and designed and perceived to subject the SRA to pressure'. Harman also questioned whether those emails can now be published.

'It is quite wrong for the government to seek to dictate to the SRA who they should be taking action against,' she said. 'It is invidious for the government to denounce solicitors who are representing claimants who believe that their rights have been violated by the government.'

Correspondence between the SRA and MoD, disclosed following an application by Leigh Day, was brought up during the seven-week SDT hearing, with defence lawyers saying they amounted to the SRA 'using disciplinary proceedings as a platform for lobbying the government for regulatory reforms and enlisting the MoD'.

Harman demanded to know whether Wright has brought up the Leigh Day case with cabinet colleagues and reminded them of the need to support an 'independent and fearless’ legal profession and not be afraid to be held to account in the courts.

She cited comments made in parliament by former prime minister David Cameron and current defence secretary Sir Michael Fallon. Speaking from the dispatch box of the House of Commons in January 2016, Fallon had said the Leigh Day claims were a 'completely unacceptable attempt to abuse our legal system to falsely impugn our armed forces'.

Harman provided a character reference to the SDT on behalf of Leigh Day senior partner Martyn Day, describing him as an 'example of what solicitors ought to be'.

She published this testimony today, saying she had not raised the issue publicly before as she did not want to undermine tribunal's independence.