Labour is calling for the Prime Minister’s ethics adviser to investigate whether a minister broke the rules following claims he billed taxpayers for political campaigning purposes.

Paul Maynard, the pensions minister, has been referred to an investigator by the parliamentary expenses watchdog over reports that he charged taxpayers when producing political materials.

The Sunday Times, which broke the story, also reported that the Blackpool North and Cleveleys MP claimed rent expenses for an office that doubles up as his local Conservative Party association’s headquarters.

Equipment claimed on public expenses by MPs is meant for constituency work rather than political purposes.

It would be indefensible if a serving minister is found to be using taxpayers’ cash to fund party political materials

Anneliese Dodds, the Labour Party chairwoman, has written to Rishi Sunak to encourage him to ask the independent adviser on ministerial interests, Sir Laurie Magnus, to look into the claims.

The senior Opposition MP said that, if the allegations are true “it is hard to see how such behaviour is consistent with the ministerial code”.

The Liberal Democrats have called for Mr Maynard to have the Tory whip suspended and be removed as a minister while a probe takes place.

The Independent Parliamentary Standards Authority (Ipsa) said the matter would be referred to the organisation’s compliance officer.

The watchdog, established after the 2009 MPs’ expenses scandal, said it would be up to the compliance officer to establish the facts of the case before deciding whether to conduct an investigation into the claims.

It said MPs can use their offices for party political purposes as long as it is part of a pre-agreed sub-letting agreement.

Ms Dodds said: “These are extremely serious allegations.

“It would be indefensible if a serving minister is found to be using taxpayers’ cash to fund party political materials.

“It is hard to see how such behaviour is consistent with the ministerial code.

“This case goes far beyond Paul Maynard.

“The party was aware of this complaint and quietly cleared him. Rishi Sunak needs to come clean on why he was cleared of wrongdoing and whether more Conservative MPs could be in similar situations.

“We are a far cry from the promise of ‘professionalism, integrity and accountability at all levels’.

“The country urgently needs a general election and change from this tired, failing Conservative Government.”

Paul believes he had the right arrangements in place

Mr Maynard had told an activist in his local Tory constituency party that it “made no sense” to create a separate office for political activity and such a move would not be a “good use” of party funds, according to The Sunday Times.

Since his election in 2010, Mr Maynard — who was made a minister in the Department for Work and Pensions in November by Mr Sunak — has spent £106,000 on printing and related costs, a bill that is higher than any Tory MP on record, according to analysis by the newspaper.

The local Tory officer told the publication that she became concerned when discovering that the constituency association did not have a return address, before later being invited to a party meeting held at Mr Maynard’s office.

According to the report, the owners of the office charge rent of £8,220 annually, granting Mr Maynard use of an office and boardroom.

He is said to have submitted invoices to Ipsa, which then pays the rent.

Laura Trott, the chief secretary to the Treasury, told Times Radio on Sunday: “Paul believes he had the right arrangements in place.

“He said he would abide by any rulings. This is ultimately a matter for Parliament.”