Senior politicians have called for Boris Johnson’s £115,000 taxpayer-funded annual allowance to be suspended after revelations in the Guardian suggested the former prime minister may have used his private office to profit from contacts he gained in office.

The government ethics watchdog, which monitors the activities of former ministers and senior civil servants, has also opened an investigation into Johnson’s newly revealed contacts and income since leaving office.

Johnson’s engagements, revealed in a major data leak from his private office, include lobbying senior Saudi officials for a firm he co-chairs and meeting with Venezuela’s president, Nicolás Maduro, after which he received more than £200,000 from a hedge fund.

The disclosures shine a spotlight on how Johnson appears to have used his private office since resigning as prime minister and the scheme that allows former UK prime ministers to claim government money to pay for expenses “arising from their special position in public life”.

The Labour peer Margaret Hodge, a former chair of the public accounts committee, who has been a longtime transparency activist, called for a full investigation.

Hodge said the Guardian’s investigation suggested that “Boris Johnson is prepared to break the ethical standards of behaviour we all sign up to as public servants”.

She said Johnson appeared to have acted “with complete impunity”, ignoring the rules that all government ministers were expected to uphold when they left office.

“We need a proper investigation to establish what happened and we must revisit the rules on both lobbying and the revolving door to make them tougher and more effective and to ensure they are implemented with proper punitive sanctions.”

The Liberal Democrats said the ex-PM should have taxpayer funds suspended and investigated. The party’s Cabinet Office spokesperson, Sarah Olney, said: “These allegations are extremely shocking.

“The government must suspend Boris Johnson’s access to the former prime minister public duty cost allowance pending a full and proper investigation.”

Labour said Johnson had “serious questions to answer about his behaviour during Covid and about his activities after being forced out of office in disgrace”.

The Labour MP for Kensington and Bayswater, Joe Powell, a longstanding campaigner on transparency, said: “Taxpayer money for former prime ministers should be treated as a privilege to support public service, not a subsidy for individuals’ business interests.

“The new ethics and integrity commission should strip Boris Johnson of his support if he’s found to have abused these privileges.”

The Labour MP Lloyd Hatton, a current member of the public accounts committee, also called for an investigation into the spending.

“These revelations raise serious questions about the potential misuse of taxpayers’ money by Boris Johnson, who appears to have squandered public money on propping up his various business ventures and commercial interests.”

The public duty costs allowance (PDCA) is a subsidy intended to support a former PM’s public duties and is not meant to be used for private or commercial activities.

A senior Cabinet Office source confirmed that Johnson had claimed funds under the scheme to pay for staff salaries in his private office. Official data shows he has claimed £182,000 in PDCA payments since leaving government.

The files raise questions about whether Johnson has blurred the lines while running the Office of Boris Johnson, a limited company established a month after he left Downing Street.

The cache of files suggest that between October 2022 and May 2024, Johnson was paid approximately £5.1m for 34 speeches. The engagements typically earn him hundreds of thousands of pounds, as well as generous expenses to cover first-class flights and stays in five-star hotels for him and his staff.

It is not unusual or against any rules for former prime ministers to travel the world delivering paid speeches, but there are restrictions on business activities they can undertake after leaving government.

These include prohibitions on lobbying contacts in foreign governments and commercial organisations that were developed while in office. Revelations from the Boris Files will place pressure on Johnson to explain how some of his recent contacts with foreign governments on behalf of commercial interest fall within the rules.

A spokesperson for the Advisory Committee on Business Appointments (Acoba), the watchdog that provides advice to former ministers on appointments, said it was investigating.

“We are currently looking at the information reported in the Guardian. Acoba has already investigated and reported breaches of the business appointment rules by Mr Johnson. Where there is evidence of further non-compliance, we will investigate.”

Johnson did not respond to multiple requests for comment. After publication, he emailed a statement to the Guardian denying that his office had misused the subsidy.

“This story is rubbish,” he said “The PDCA has been used entirely in accordance with the rules. The Guardian should change its name to Pravda.”