It has proved fortunate for Boris Johnson that his government chose last year to drop plans to cap how much MPs could make from second jobs outside parliament. Nine months later, the former prime minister has benefited from more than £2.5m in earnings from speeches, hospitality, free accommodation, gifts and donations to his new company, The Office of Boris Johnson. His haul in just over four months means he is topping the leaderboard of MPs in terms of both donations and cash from work unrelated to his job in the House of Commons in the last year. Speculation is now rife that Johnson will use the money coming into his office to launch a political comeback – emphatically denied by his allies – especially with Rishi Sunak failing to make much headway in the polls. This has only intensified after it emerged this week that his office has taken £1m from Christopher Harborne, an investor in crypto and aviation fuel based in Thailand, who previously donated £6m to the Brexit party, now known as Reform UK. “Why would Boris need a £1m donation if he was not planning a political comeback?” asks Labour’s Diane Abbott. His allies say his company undertakes no commercial work and the money will be used to fund his work in public life. But the truth is that if Johnson does want to return to frontline politics then some of the largesse he has benefited from over the last few months may prove an obstacle. Sunak entered No 10 promising an ethical overhaul after the Owen Paterson scandal linked to the former MP’s second job, public anger over Partygate and the furore over Johnson initially using a Tory donor to fund the overhaul of the No 11 flat. If he was serious about returning, Johnson might have attempted to show he had learned from past mistakes and take extreme care to avoid any controversy over the sources of his funding. However, his lifestyle continues to be subsidised by a wealthy Tory donor, with Lord Bamford and his wife giving him use of a £20m London townhouse and a cottage in the Cotswolds. He has also taken more than £250,000 for a speech to a conference in Singapore about blockchain, the technology behind crypto currency, funded by a little-known Hong Kong based startup called ParallelChain Lab. Turning to Harborne, little is known publicly known about the technology investor, whose name features in the Panama Papers as an intermediary of companies linked to offshore accounts, and who also goes by the Thai name Chakrit Sakunkrit. But he is believed to have been a backer of a leading cryptocurrency and a crypto exchange, as well as owning AML Global, an aviation fuel business. His bankrolling of Nigel Farage’s Brexit party also places him firmly on the hard pro-Brexit right of the Conservative party. A narrative about the betrayal of Brexit is Johnson’s most likely source of support within the Conservative party for a comeback, especially if Sunak does a deal on the Northern Ireland protocol that angers the European Research Group wing of the party. Such argument has already been put forward by one of his former supporters, Peter Cruddas, who told the Observer last month that the Tories are under threat from a rightwing insurgency after a “drag to the left” under Sunak. But whether Johnson is the person to front that campaign is still unclear. Many Conservative MPs fear he would continue to dog the party with yet more financial or ethical controversies. He also has the privileges committee inquiry into whether he misled the Commons over Partygate to contend with, and the Covid inquiry into the government’s handling of the pandemic. He may have had the necessary 100 MPs – less than a third of the parliamentary party – to notionally have fought Rishi Sunak for the leadership back in the autumn but he did not have enough support to have governed effectively. His activities since leaving No 10 are not likely to have convinced the doubters that he has changed.