Boris Johnson earned £1.3m in three years

Boris Johnson earned just short of £900,000 in freelance earnings on top of his six-figure mayoral salary in the first three years at City Hall, figures published by the Conservative mayor reveal.

In the past 12 months alone, Johnson, who earns £250,000 for a Daily Telegraph column, received an additional £139,625 in freelance earnings, alongside his £143,911 mayoral salary.

The scale of Johnson's earnings will fuel claims by his rival Ken Livingstone that the Conservative candidate stands to benefit significantly from George Osborne's decision to scrap the 50p top rate of tax – a move for which Johnson has strongly lobbied.

Johnson was elected mayor in May 2008. From the period covering 2008-2009 to 2010-2011, he earned £896,643 on top of his mayoral salary. Last year, he earned £473,280, on which he paid £210,410 in income tax, and £3,339 in national insurance contributions, giving him total earnings of £1.3m over three years.

The Conservative candidate released the details to deliver on a joint pledge made by the mayoral rivals late on Wednesday night on live television during a debate on BBC2's Newsnight. The candidates agreed to publish details of their financial affairs in a bid to settle an ongoing row between Johnson and Livingstone over their respective tax arrangements.

But while Johnson honoured his side of the bargain, Livingstone refused to follow suit unless the candidates met certain criteria.

He insisted the financial details of candidates' partners must also be included and an independent body appointed to publish the details side by side.

The Green party candidate for the 3 May election, Jenny Jones, suggested the deal on Newsnight as a means of drawing a line under a row that blew up in a lift when Johnson turned on Livingstone and called him a "fucking liar" after another live studio debate on Tuesday.

Jones, who witnessed the lift row, said: "I'm just wondering why we don't end this by everybody just publishing what they earn and then what they pay in tax. Why don't we just bring it all out into the open? Then there are no arguments and we can talk about some of the issues we have all got in our manifesto."

Johnson at first appeared to be reluctant, but agreed after Livingstone threw down the gauntlet, saying: "I'm happy to publish the details of everything I have earned in the last four years. Are you going to do the same?"

By the next morning, Livingstone issued the terms under he was prepared to publish, in the light of the attention that has been focused upon "my income tax and that of my wife", Emma Beal.

Livingstone has been stung by accusations that he has been hypocritical in denouncing those who avoid tax while having set up a private company, Silveta, to channel his earnings, so he was liable to pay corporation tax at 20% rather than income tax at a higher rate. He insists the company was set up because he employed his wife to type up his 700-page autobiography, and two other members of staff working on his election campaign, and has repeatedly alleged that Johnson had similar arrangements.

In his Thursday morning statement, Livingstone said: "I will lodge the details for the last four years with an independent body or individual, to be published simultaneously when all four main candidates have provided them. I will set out income to my company over the last four years, how much my wife and I received, and how much tax was paid. Full household income and tax must be released by all candidates because the question of the overall household income and tax has continuously been the subject. This fully meets the terms agreed on Newsnight."

Johnson said candidates who signed up to the deal should "keep their promises". "Last night every candidate gave an unequivocal promise on national TV to release all their earnings, whether through a company or not, and all the income tax they paid on all those earnings," he said. "I have done that today and I would expect, and am sure Londoners would also expect, all candidates to keep their promises. As I have always said in this election, Londoners should be able to trust their mayor."

Brian Paddick, the Liberal Democrat candidate, who also appeared on Newsnight, released provisional figures prior to pulling together all the details, while Jones's campaign was hoping to have her details in the next few days.

Paddick, a former senior officer at Scotland Yard, operates as a sole trader. His earnings include an annual police pension of £63,397 a year and other earnings which vary by year, on which he pays full tax.

In 2010-11, he earned an additional £13,355, making £76,804. A spokesman for Paddick said: "Brian Paddick has nothing to hide and is very happy to be open and transparent about his income and tax returns as a registered sole trader. His figures show he has never attempted to use any complex arrangements to dodge paying anything less than full tax on his earnings."

The spokesman added that Livingstone's terms for publishing were "clearly an attempt to delay full transparency of his own tax arrangements. What has he got to hide?"

Labour said publishing household incomes was the only way to ensure the process was "open and fair".

In a letter sent this morning to the agents of the other campaigns, Ken Livingstone's campaign director, Patrick Heneghan writes: "We believe household publication is necessary for full disclosure as the question of Ken's income and his wife's income and their tax has been central the coverage of this issue. Publication of Ken's returns alone will not address many of the questions that have been raised.

"The only way to answer all the questions about this issue and to move the debate on the real issues facing London is for full household income disclosure. This should apply to all the candidates equally to avoid any further questions about the income and tax affairs that may or may not be applicable to them through their households. The same principles need to be applied to all the candidates if this process is to be seen as open and fair."