Gordon Brown has revealed he donated more than £1m which he earned from second jobs while working as an MP to charity.
The former Labour prime minister, who served as an MP for 20 years, warned that conflicts of interest arising from MPs' additional work are “bringing the House of Commons into disrepute”.
Watch: Cut to universal credit uplift 'not the right way to save government money', Gordon Brown says
He made the remarks amid ongoing debate of the Owen Paterson lobbying scandal, which has triggered a broader conversation about the conduct of politicians in parliament.
On Wednesday, Labour demanded in inquiry into the conduct of Tory MP Sir Geoffrey Cox after a video emerged appearing to show him undertaking external work from his Westminster office.
Sir Geoffrey has been paid more than £1m in the past 12 months in addition to his MP salary for work as a lawyer for clients including the British Virgin Islands.
Speaking to BBC Radio 4's Today, Brown said he "never" kept any additional money for himself.
“I gave all the money to charity and I’ve always done that, I’ve never taken any money for myself," he said.
"All I’ve got to live on is the pension, that is a good pension that I’ve got from being an MP.”
Watch: Who is Sir Geoffrey Cox? Tory MP at centre of new sleaze row - but what has he been accused of?
His comments come in stark contrast to the behaviour of his fellow ex-PMs such as Theresa May, who was paid £11,700 per hour for virtual speeches during the pandemic.
Earlier this year, David Cameron came under fire after it emerged he was using his position and connections as a former prime minister to lobby the government on behalf of the private financial firm, Greensill Capital.
Brown, who is an advocate for equitable access to vaccines globally and now serves as special envoy for global education at the United Nations (UN), backed an “outright ban” on MPs “using a public office for private gain”.
“What I’m talking about is using public office, being an MP, for private gain and for pushing private interests – that’s what’s got to be outlawed," he said.
“You can’t prevent an MP writing a newspaper article or giving a speech, but what you can do is say, where the private interest is at stake you cannot use your public office, whether you’re an MP or an ex-government minister, to advance a private cause.
“I do believe that, unless the prime minister takes a grip of this issue, this parliament will be remembered for the extent to which sleaze has (been) allowed to become a feature of British politics again.”
Brown also warned that the behaviour of MPs risked destroying public trust in politicians,
“Now, we will have to deal with these conflicts of interest because they’re bringing the House of Commons into disrepute, appointments to the House of Lords for people with commercial interests are bringing the House of Lords into disrepute, and people are losing trust in British politics and something has got to be done," he said.
Since the Paterson scandal, further stories have emerged about the conduct of MPs, including Sir Geoffrey Cox.
The Times reported the practising barrister used his MP office in September to participate remotely to advise the British Virgin Islands over a corruption probe launched by the Foreign Office.
Sir Geoffrey defended his decision to work with the island group, and said he did not believe he had broken any rules.
The Met police confirmed this week that they were "considering" reports of corruption both by the prime minister and the Conservative party following a letter from SNP MP Pete Wishart, who claimed the government were offering "cash for honours" for the House of Lords.
Several former Conservative treasurers, and donors who gave more than £3m to the party, have received peerages since the Conservatives took office in 2010.
Watch: Boris Johnson refuses to apologise for handling of sleaze scandal