The Conservatives have written to the parliamentary commissioner for standards calling for an investigation into allegations that Keir Starmer may have failed to declare “potentially thousands of pounds’ worth” of support from campaign group Labour Together when he ran for the Labour leadership in 2020.

This is the third investigation that the Tories have demanded within 48 hours in relation to a controversy about Labour Together, a group originally run by Morgan McSweeney, who is now Starmer’s chief of staff. Labour Together was set up to fight Corbynism in the party when Jeremy Corbyn was in charge and it eventually played a crucial, though largely behind-the-scenes, role in helping Starmer to become leader in 2000.

The group failed to declare donations worth £730,000 to the Electoral Commission and was investigated in 2021 and fined. These facts have been known for years. But interest in the story has been revived by publication of a new book, The Fraud: Keir Starmer, Morgan McSweeney, and the Crisis of British Democracy, by Paul Holden.

On Sunday the Tories demanded a police investgation into claims that McSweeney deliberately did not disclose the donations. McSweeney has said the non-disclosure was inadvertent, the result of an administrative error.

Last night Kevin Hollinrake, the Tory chair, wrote to the Electoral Commission demanding an inquiry.

And this morning Hollinrake has released the text of a letter to Daniel Greenberg, the parliamentary commissioner for standards. In the letter he says:

Between January and April 2020, Labour held a leadership contest. Evidence from that period suggests that the prime minister accepted potentially thousands of pounds’ worth of advice and polling via the members’ association Labour Together. A review of his register of members’ interests for that time reveals no record of these donations. The parliamentary rules are clear that “support in kind” from Labour Together should have been declared, but it was not.

In 2021, the Electoral Commission fined Labour Together for failing to report donations covering the period 2017 to 2020. New evidence has since come to light which raises questions as to whether this failure was deliberate, in an attempt to mislead the Electoral Commission. At the time, the prime minister’s now Chief of Staff, Morgan McSweeney, was a director at Labour Together and responsible for legal compliance.

This new information prompts a re-evaluation of Labour Together’s activities between 2017 and 2020. Labour Together itself has claimed that it “helped to rally the party membership behind Keir Starmer” and that it “united the party behind Keir Starmer’s leadership campaign”.

Reports indicate that Labour Together, under Morgan McSweeney, spent hundreds of thousands of pounds on polling, which was then used in Starmer’s leadership campaign. This support was not declared.

Labour Together also provided written materials and strategic support. The organisation was involved in preparing Sir Keir’s first speech as Labour leader, yet this assistance does not appear in the Register. Notably, at this time the chancellor, Rachel Reeves, did register donations for the “provision of research and writing services”, yet the prime minister did not.

Hollinrake suggests Starmer broke the rules saying MPs must declare support worth more than £1,500, including “support in kind”.

In response, a Labour source said:

Neither Keir, nor his leadership campaign accepted monetary or in kind donations from Labour Together during the leadership election.

Commenting on the Tory approach to the Electoral Commission, a commission spokesperson said the issue had been “thoroughly investigated” in 2021 and had been “satisfied that the evidence proved beyond reasonable doubt that failures by the association occurred without reasonable excuse”. She added: “Offences were determined and they were sanctioned accordingly.”