Gordon Brown has suggested former prime ministers should be banned from lobbying on behalf of businesses for five years after leaving Downing Street.
The ex-Labour premier proposed such a measure if existing rules can’t be tightened to stop departed ministers from lobbying for commercial purposes.
It follows the actions of Mr Brown‘s predecessor as prime minister, David Cameron, who approached serving ministers and officials about the involvement of Greensill Capital in government-backed financial support schemes during the coronavirus crisis.
After weeks of silence, Mr Cameron this weekend finally commented on the matter and accepted there were "important lessons to be learnt", although he stressed he had broken "no codes of conduct and no government rules".
Asked about Mr Cameron’s remarks, Mr Brown told BBC Radio 4’s Today programme: "I can’t comment on the individual detail of this, but for me there are principles about public service – it cannot ever become a platform for private gain.
"Ministers must never be lobbying, former ministers, prime ministers, must never be lobbying for commercial purposes. Current ministers should not be entertaining such lobbying.
"And if we can’t succeed in achieving this stopping by the sort of flexibility of the rules, we are going to have to pass laws to make sure that at least for say five years, no serving or former prime minister or minister, is ever lobbying for any commercial purpose within government.
"It simply brings public service into disrepute."
Mr Brown remembered having to deal with the 2009 MPs’ expenses scandal while in Number 10, adding: "That brought anybody who was in public service into disrepute and was under attack.
"This will happen in the same way with lobbying if we don’t actually do something to pass laws to prevent this happening."
Before succeeding Mr Brown in 2010, Mr Cameron predicted political lobbying was the "next big scandal waiting to happen" following the MPs’ expenses row and – in the same speech – accused Mr Brown of "blocking reform".
While in government, Mr Cameron went on to introduce laws to enhance the transparency of those seeking to lobby ministers and civil service officials on behalf of a third party.
However, Mr Cameron was last month cleared by the watchdog set up by that 2014 legislation after it concluded he had not fallen within the criteria that required registration.
Sources close to the former prime minister pointed out, because he was an in-house employee of Greensill, Mr Cameron did not need to be listed on the Register of Consultant Lobbyists.
Mr Brown has been a member of an advisory board for international investment firm Pimco since 2015 – his first private sector role since resigning as prime minister – and is now also an adviser for Swiss private equity firm Partners Group.
The fees for his private sector roles are said to be paid to the Office of Gordon and Sarah Brown, the business set up to support the couple’s charity work.
There is no suggestion Mr Brown has lobbied UK government ministers on behalf of the firms.
Meanwhile, senior Conservative MP Tobias Ellwood – who served in Mr Cameron’s government – suggested the "spirit of the rules" on lobbying had been broken over the Greensill scandal.
"I think that can be an interpretation here and I think that’s correct, which is why [Mr Cameron] has come out with his own statement," he told Sky News.
"A lengthy statement to clarify the fact that what he did wasn’t correct and that if he had an opportunity to do it again he would approach it very, very differently indeed.
"So, yes, the spirit of the rules need to be recognised as much as the rules themselves."