Guardian analysis shows frontrunner to replace Theresa May has done well since quitting government last year

Boris Johnson has pocketed nearly £700,000 for speeches and newspaper columns since he quit government less than a year ago, while other prominent Brexiters have received tens of thousands of pounds while cheerleading Britain’s exit from the EU.

The former foreign secretary, who is the frontrunner to succeed Theresa May as prime minister next month, was paid £407,895 for just eight speaking engagements – a rate of £20,000 an hour.

His most recent paid speeches, disclosed in the register of MPs’ financial interests on Wednesday, included a £25,540 insurance brokers’ gig in Manchester where he confirmed his Tory leadership bid on 16 May.

Johnson has pledged to take Britain out of the EU “deal or no deal” by 31 October as he ramps up his campaign to replace May in a ballot of Tory members next month. The new prime minister is expected to be announced in the week beginning 22 July.

A Guardian analysis of financial declarations shows Johnson has done rather well since he resigned as foreign secretary in protest at May’s Chequers deal last July.

On top of his £407,000 for speeches, the Tory MP resumed his £275,000 a year Telegraph contract and received a further £3,500 for four other newspaper articles, plus £27,000 in book royalties, taking his total income to £712,500 – almost 10 times his yearly MP’s salary of £79,000 for representing Uxbridge and South Ruislip in parliament.

Johnson’s best-paying gig was a speech about Brexit for India Today at the five-star Taj Palace hotel in New Delhi, India, for which he received £122,899.74 in March. He used that address to attack Brussels and critics of Britain’s departure from the EU, which he described as an “anti-democratic, over-legislating, job-destroying machine”.

Should Johnson become prime minister, he will have to forfeit his substantial second income and survive on the basic salary of £150,402 for the top job in government. The ministerial code prohibits those in government from being paid for speeches or media articles “of an official nature or which directly draw on their responsibilities or experience as ministers”.

Quick guide Tory party leadership contest Show Hide What happens next in the Tory party leadership race? As she announced on 24 May, Theresa May stepped down formally as Conservative leader on Friday 7 June, although she remains in place as prime minister until her successor is chosen. In a Conservative leadership contest MPs hold a series of votes, in order to narrow down the initially crowded field to two leadership hopefuls, who go to a postal ballot of members.

How does the voting work? MPs choose one candidate, in a secret ballot held in a committee room in the House of Commons. The votes are tallied and the results announced on the same day. In the first round any candidate who won the support of less than 17 MPs was eliminated. In the second round anybody reaching less than 33 votes was eliminated. In subsequent rounds the bottom placed contender drops out until there are only two left. The party membership then chooses between them. When will the results be announced?

The postal ballot of members has begun, and the Tory party says it will announce the new prime minister on 23 July.. Photograph: Neil Hall/EPA

However, upon leaving office they are free, within reason, to cash in on their role. Payments of over £100 must be registered every 28 days with the parliamentary commissioner for standards, who then publishes a fortnightly register of all MPs’ financial interests.

Johnson is by far the biggest earner on the highly-lucrative Brexit speaking circuit, but other leading leave campaigners have also received large sums.

David Davis, the former Brexit secretary, has been paid £64,000 for four speeches and enjoyed trips to Davos, Munich, Washington DC and Oklahoma bankrolled to the tune of £17,300, including one funded by a lobbying firm owned by the Tory strategist Sir Lynton Crosby, since he quit government last July.

Davis’s five-figure speaking gigs are on top of his two part-time business posts, advising the pro-Brexit digger firm JCB and the German manufacturer Mansfelder Kupfer und Messing, for which he receives about £74,000, and his full-time job representing Haltemprice and Howden in parliament.

The former Tory leader Iain Duncan Smith, another arch-Brexiter, has been paid £75,380 for speeches and newspaper articles since the EU referendum in June 2016, of which £56,580 were for speaking engagements.

The environment secretary, Michael Gove, pulled in £25,000 for three speeches and enjoyed £30,000-worth of foreign trips to Dubai, Japan, Georgia and Washington DC in the 11 months after he left government in July 2016. He also earned £150,000 a year as a Times columnist in that period.

One of the most prominent backbench Eurosceptics, Jacob Rees-Mogg, has received more than £28,000 for columns and media appearances since the referendum. The Tory MP, who chairs the influential European Research Group, was paid in champagne for one speech by Global Media, the owner of LBC radio where he hosts a fortnightly phone-in. The register of interests, first disclosed in April, states that he “received 12 bottles of champagne with a total value of £323.52”.

Dominic Raab, another former Brexit secretary, was paid nearly £11,000 for newspaper columns since the EU referendum, not including the five months he was in government.

Some prominent remain-supporting MPs have also been paid for speeches and media work but the sums involved were, in most cases, much smaller. The veteran Conservative MP Ken Clarke received £21,300 for four speeches in under a week last month, the latest disclosures show.

Chuka Umunna, the former Labour MP who quit the new Change UK party this week, has a £13,200-a-year weekly column with the Independent, and received £500 from the BBC for appearing on This Week and Any Questions last year. Vince Cable, the Liberal Democrats leader, received £3,500 for a speech and a newspaper article last year but donated the money to charity.