Dominic Cummings broke government rules by failing to seek permission from the revolving door watchdog before setting up his Substack blog and offering consultancy services, a minister has said.

In one of his last acts as a Cabinet Office minister, Nicholas True said in a letter to Eric Pickles, the chair of the Advisory Committee on Business Appointments (Acoba), that “Mr Cummings, in this and other matters, did not follow the [business appointment rules] correctly”.

As a former senior special adviser, Cummings was required to consult Acoba before taking up any appointments or employment in the two years after he left Downing Street in November 2020.

But Cummings did not seek the committee’s permission before launching his paid-for Substack blog in June 2021, where he offered himself as a consultant. “Fees slide from zero to lots depending on who you are / your project…” he wrote.

The failure to consult Acoba led to Lord Pickles writing to Michael Gove, then the senior minister in the Cabinet Office, in July 2021 notifying the government of the breach.

Lord True took 14 months to respond to Pickles, meanwhile responding to a number of letters about other individuals who likewise breached the rules but were not the former chief adviser to the prime minister.

Despite the government finding that Cummings broke its rules, which are administered by Acoba, Cummings is unlikely to be affected by the limited sanctions that can be imposed, unless he finds himself lined up for an honour, a peerage or a public appointment.

“Mechanisms are now in place for breaches of the rules to be taken into account in the award of honours and we are seeking to develop the same system with the independent House of Lords appointments commission,” True said. “We are also currently considering how to implement the same approach in relation to public appointments.”

True admitted that “the current system offers too few avenues to achieve effective redress” where former ministers and officials fail to fulfil their responsibilities “in good faith”.

He said he agreed with Pickles that “the review of business appointment rules needs to be accelerated and completed”. In July 2021, the then Cabinet Office minister Chloe Smith pledged “an update to the rules later this year”. By December 2021, ministers had revised the promise to provide “in the new year … an update to its work to reform the business appointment rules”.

Cummings did not respond to a letter from Pickles asking for an explanation of why he failed to consult the committee. Acoba declined to consider a later application by Cummings for permission to work as a consultant for a firm whose identity it redacted, citing his failure to respond to its correspondence.

The redacted firm was mistakenly revealed by Acoba officials as being Babylon Health after it left “Babylon” in the filename of its letter to the Cabinet Office. Cummings had worked for the AI healthcare firm before joining Boris Johnson in Downing Street in July 2019.

Cummings did not respond to a request for comment.