The Labour minister Josh Simons has resigned from the government after the Guardian revealed that he falsely linked reporters to a “pro-Kremlin” network in emails to GCHQ despite having claimed to be “surprised” and “furious” about a PR firm’s investigation into their journalism.

Simons, who had been a Cabinet office minister, previously ran the thinktank Labour Together. He quit on Saturday, saying his position in office had become “a distraction from this government’s important work.”The Makerfield MP had faced mounting pressure over his role in Labour Together’s commissioning of the lobbying and public affairs agency APCO to investigate journalists reporting on the thinktank’s failure to disclose political donations.

Simons faced a formal investigation by the prime minister’s independent adviser on ministerial standards, Sir Laurie Magnus. Magnus concluded that Simons had not breached the ministerial code, but that there was a “distraction and potential reputational damage” in Simons remaining in the government.

Earlier this month, the Guardian revealed Simons had personally commissioned and reviewed APCO’s report on journalists looking into the group’s funding.

After the Sunday Times reported that APCO’s report made baseless allegations about its journalist Gabriel Pogrund’s faith, upbringing and personal and professional relationships, Simons said he was “surprised and shocked to read the report extended beyond the contract by including unnecessary information” on Pogrund.

But on Friday the Guardian revealed that Simons and his chief of staff had emailed the National Cyber Security Centre (NCSC) after the APCO report, naming Pogrund and his Sunday Times colleague Harry Yorke and suggesting their story could be linked to a Russian disinformation campaign.

They also sent a truncated version of the APCO report to NCSC officials and claimed that Paul Holden, a freelance journalist who also investigated Labour Together, could be linked to “people known to be operating in a pro-Kremlin propaganda network with links to Russian intelligence”.

There is no credible evidence any of the journalists were involved in a pro-Russian campaign.