The owner of the London Evening Standard has defended his appointment of former Chancellor George Osborne as the paper’s editor in the face of criticism from both Labour and Conservative ranks.

Evgeny Lebedev, who has owned the free daily newspaper for eight years, said critics should “wait to see a paper before judging”, adding that Mr Osborne would provide a “more effective opposition to the Government than the current Labour Party”.

It comes after critics from both the main parties said the move raised fresh questions over existing parliamentary systems for preventing conflicts of interest, and cast doubt on whether Mr Osborne could continue as an MP for Tatton.

Responding to the criticism on Twitter, Mr Lebedev, who is also proprietor of The Independent, said: “Sad old commentariat. Wait and see his paper before judging. Tories saying he will criticise the Government now. Labour say he is a Tory stooge. So, which is it?!

“Frankly George Osborne will provide more effective opposition to the Government than the current Labour Party. And will stand up for the interests of London and Londoners.”

Fellow former Tory frontbencher Michael Gove, a columnist for The Times, meanwhile wished Mr Osborne well in his new role, adding that he welcomes “high-quality recruits to the world of journalism”.

Following the announcement that the former Chancellor is to replace outgoing editor Sarah Sands, Labour called for an inquiry with the official watchdog that vets new jobs taken by senior public figures into whether Mr Osborne broke rules for former ministers by failing to clear the appointment.

Shadow minister Andrew Gwynne wrote to John Manzoni, permanent secretary at the Cabinet Office, asking him to investigate whether Mr Osborne – who was sacked by Theresa May in June – had breached the ministerial code of conduct.

In his letter, he said Mr Osborne was required to refer any new job he intended to take within two years of leaving office to the Advisory Committee on Business Appointments (Acoba) before accepting it.

Labour MP Clive Lewis meanwhile said he would be writing to Acoba directly about the appointment.

“There are really serious questions about conflicts of interest. The rules are clear. Osborne has shown total contempt for those rules, and I am calling for them to be enforced without fear or favour,” said the MP.

Mr Osborne is also facing growing pressure to stand down as the MP for Tatton, which is 190 miles from the capital, amid questions from constituents over the time he will be able to dedicate to the job, given his five other paid and unpaid roles.

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The MP has registered a series of other jobs since leaving the Treasury, including a contract with the investment company Blackrock, which will see him earn £650,000 a year for one day’s work a week.

After the Evening Standard appointment was announced on Friday, Mr Osborne said in a statement: “I am proud to be a Conservative MP, but as editor and leader of a team of dedicated and independent journalists, our only interest will be to give a voice to all Londoners.”