MPs in safe seats are far more likely to have taken up second jobs than their colleagues in marginal constituencies, according to new analysis that has led to renewed calls for reforms to Britain’s voting system. In findings that undermine Boris Johnson’s suggestion that voters who disapprove of their MP’s outside work can simply unseat them at an election, the research found that more than three in five of the 103 MPs with second jobs had majorities of more than 10,000 votes. Some 87% had majorities of more than 3,000 votes. The research, by the campaigning group Best for Britain, found that almost all of the MPs who earn more than their £82,000 parliamentary salary from a second job have majorities in excess of 17,000 votes. It will also anger Tories in newly won “red wall” seats, where majorities are more precarious. The group has been the most frustrated by colleagues taking up second jobs on top of their role as an MP. Several have complained that only those in safe Tory areas have taken on extra roles. Geoffrey Cox, the former attorney general who has earned almost £6m in addition to his MP’s salary since entering parliament, was among those who claimed that his constituents would simply vote him out if they disapproved. Cox faced a new wave of criticism after it emerged that he had voted remotely from the British Virgin Islands while advising its government on corruption allegations.Cox has a 25,000 majority. Of the nine MPs who earn more from their second jobs than from their parliamentary salary, seven have majorities in excess of 17,000 votes and all are Conservative MPs. Overall, 83% of all MPs with second jobs are Conservative MPs. The Commons standards committee is now examining the issue of second jobs and is to publish recommendations. Clive Lewis, a Labour MP who backs electoral reform, said the correlation between MPs with safe seats and second jobs highlighted the problem with the first-past-the-post voting system. “First past the post has clearly given some MPs a brass neck and the leadership of opposition parties must accept that the only way they can give the public a realistic opportunity of unseating the worst offenders is by working together to secure a fairer voting system,” he said. Naomi Smith, chief executive of Best for Britain, said: “First past the post delivers disproportionate outcomes, doesn’t represent the majority opinion, and delivers safe seats for too many MPs emboldening those who put personal financial gain ahead of voters.”