Calls have been made for the Prime Minister to suspend the whip from a minister while claims he used his taxpayer-funded constituency office to campaign for the Conservative Party are reviewed.

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 for an office that doubles up as his local Tory association’s headquarters.

Rishi Sunak must suspend the whip and Paul Maynard as a minister whilst these extremely serious allegations are investigated

The Liberal Democrats urged Prime Minister Rishi Sunak to suspend the Tory whip from Mr Maynard and remove him as a minister while “these extremely serious allegations are investigated”.

Labour said “any suggestion that taxpayer money has been misused must be thoroughly investigated”.

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 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 party officer told the newspaper she became concerned when discovering that the constituency association did not have a return address, before later being invited to a local 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 the Independent Parliamentary Standards Authority (IPSA), the expenses watchdog, which then pays the rent.

Donors wanting to give money to the local party had to deposit money in Mr Maynard’s own bank account or that of his chief of staff, the report states.

IPSA, the watchdog established after the 2009 MPs’ expenses scandal, states that all claims submitted by lawmakers must follow four principles, with one of them being that they can “only claim for expenditure for parliamentary purposes”.

They must also adhere to the MPs’ Code of Conduct, including the seven principles of public life – which include openness and honesty.

Daisy Cooper, the Lib Dem deputy leader, said: “Rishi Sunak must suspend the whip and Paul Maynard as a minister whilst these extremely serious allegations are investigated.

“These latest allegations are yet another sore reminder of the number of times that senior Conservatives have shown utter contempt for the rules.

“The Conservative Party has proven itself completely unfit to be in office. We need a general election now.”

Anneliese Dodds, the Labour Party chairwoman, said: “These are extremely serious allegations.

“Any suggestion that taxpayer money has been misused must be thoroughly investigated.

Are there other Tory MPs seemingly using taxpayer money to promote themselves and the Conservative Party?

“There are serious questions to be answered by Rishi Sunak and the Conservative Party.

“How was this allowed to happen? Why was the complaint against Mr Maynard not taken seriously?

“And are there other Tory MPs seemingly using taxpayer money to promote themselves and the Conservative Party?

“Rishi Sunak’s promise of professionalism, integrity and accountability was in tatters long before these revelations. We urgently need a general election and change with Labour.”

An IPSA spokesman said: “We will be referring this matter to IPSA’s compliance officer.”

IPSA 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.

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

Mr Maynard has been contacted for comment by the PA news agency.

In a statement issued to The Sunday Times, he said there were “financial agreements in place with IPSA over the ad-hoc use of my constituency office by the local Conservative Association”.

He told the newspaper: “I believe that these arrangements are appropriate, but will be seeking clarification from IPSA to ensure this is the case.

“I will, of course, abide by any findings they make and ensure that any payments deemed necessary can be made promptly.”

Mr Sunak is already facing a potential by-election contest in Blackpool after an MP was caught in a lobbying sting.

Blackpool South MP Scott Benton was caught by The Times offering to lobby ministers and table parliamentary questions on behalf of gambling investors.

Mr Benton has said he will appeal against a recommended 35-day suspension made by the Commons Standards Committee.

If the Commons backs the punishment, it could leave the former Tory MP – who was stripped of the whip after the allegations surfaced – facing a by-election.