Sir Keir Starmer’s communications chief Tim Allan owns a minority stake in a lobbying firm and still discusses government activity with a senior consultant at the company, Sky News can reveal.

The relationship between Tim Allan, Tom Baldwin and Strand Partners has led to accusations of a perception that one of Downing Street’s most senior figures has a conflict of interest – a potential breach of the special adviser code.

Tom Baldwin is a consultant for Strand Partners, a lobbying firm partly owned by Mr Allan, the government’s executive director of communications.

Multiple sources have told Sky News that Mr Allan and Mr Baldwin have discussed government affairs and politics since Mr Allan joined Number 10 in September. This is not challenged by Downing Street, who say the pair speak in Mr Baldwin’s capacity as a journalist.

Mr Baldwin is also Sir Keir’s biographer, a commentator and has appeared on Sky News.

As part of his role for Strand Partners, he has spoken at private briefings for Strand’s corporate clients about the inner workings of government.

There is no suggestion that Mr Baldwin – who is not a lobbyist – or Strand Partners have done anything wrong.

The revelations about Mr Allan have led to cross-party calls for an investigation and a member of Labour’s ruling National Executive Committee to demand he gives up his 10% shareholding in Strand Partners.

Zack Polanski, the Green Party leader, told Sky News: “I think it’s extraordinary that someone still has shares who’s at the heart of Downing Street… I think there’s lots of questions still to be asked, I think it’s important to know what these supposed appropriate mitigations are, what exactly are those and do they pass the public sniff test?”

Mr Allen is bound by the code of special advisers that says: “Special advisers must ensure that no conflict arises, or could reasonably be perceived to arise, between their official duties and their private interests, financial or otherwise.”

The code also says: “Special advisers must not misuse their official position or information acquired in the course of their official duties to further their private interests or those of others.”

Mr Baldwin and Mr Allan are understood not to discuss Strand Partners business. Mr Allan has undertaken to not take dividends or get involved in the running of the company while he is in government, and resigned as chairman on his appointment to Number 10 at the start of September.

But other lobbyists told me they are jealous of this level of access, giving rise to the perception of a conflict of interest.

Opposition parties are seeking an investigation. Lisa Smart, a Liberal Democrat frontbencher, said: “I’ve written to the cabinet secretary today because this appears to be a clear conflict of interest right at the heart of government.

“It cannot be the case that the executive director of communications for the government has shareholdings in a lobbying firm and is continuing to have conversations with senior consultants at that firm.”

Kevin Hollinrake, Conservative Party chairman, said: “[There] should be a full Cabinet Office investigation. I think the public need to see there are no conflicts of interest and no perceived conflicts of interests, and that’s not where we are right now.”

The member of Labour’s National Executive Committee said: “This is a massive conflict of interest when we promised integrity to the British public. The first thing he has to do is give up his shareholding.”

Since Mr Allan took up his role in September, Mr Baldwin has been allowed by Treasury officials in Downing Street to attend at least one restricted event with Chancellor Rachel Reeves, her news conference on the budget last week.

Mr Allan denies knowing about this in advance and said this is part of a multi-interview feature for a newspaper, but it is a sign of how close Mr Baldwin is with members of the government.

A Labour spokesperson said: “The allegation that Tim Allan has done anything to benefit Strand whilst in Number 10 is categorically false.

“Tom Baldwin is an established journalist, author and commentator, who regularly appears on Sky News. Any interactions with him are in his capacity as a journalist and have not related to Strand, its business or its clients.”

A Cabinet Office spokesperson said: “There is a rigorous process to capture any potential conflicts of interest, and ensure appropriate mitigations are in place to reflect specific circumstances. Ahead of his appointment, Tim Allan fully complied with this process.

“This is set out in the Special Adviser Code of Conduct and lists of special adviser interests are published annually.”

A Strand Partners spokesman said: “Tom Baldwin is a journalist and the biographer of the prime minister. He does not engage in government relations for Strand and this is not part of his terms of engagement with us.

“Tim Allan sought advice on his interests from the Cabinet Office and followed every element of the advice received. He receives no financial benefit from Strand and is not involved in our operations.”