Labour demands answers over George Osborne's Evening Standard job Labour demands answers over George Osborne's Evening Standard job George Osborne is laughing at us as he takes his Evening Standard job | Aditya Chakrabortty

George Osborne

George Osborne’s appointment at the London Evening Standard while remaining a Conservative MP could be a potential conflict of interest with government advertising budgets, Labour has said.

The row came as former prime minister Tony Blair praised the appointment, saying he hoped it would be a good move for the MP. “I don’t know if having both of those jobs is doable, but it’s a great thing for the Evening Standard,” Blair told the BBC’s Andrew Marr show. “Why not? He’s a highly capable guy and it’ll make politics __more interesting.”

On Monday, former shadow cabinet minister Clive Lewis will table questions in parliament to each government department asking them to spell out their advertising spend with the newspaper since 2010, as well as future spending plans.

The Treasury, where Osborne was chancellor for six years, had the largest budget for newspaper advertising of any government department in the last financial year, spending __more than £2.6m in the Daily Mail, Sun, Daily Mirror, Times and Guardian titles alone, according to the department’s own figures from December. The Evening Standard was not included in the figures.

“It is not just about the obvious political conflicts of interest but the commercial interests involved as well,” Lewis said. “I am demanding that the government tell us just how much the Evening Standard earns in advertising revenue from them, and especially from the former chancellor’s old department, the Treasury.

“There are a real questions to answer, but Osborne has brazenly flouted the rules by applying for, accepting and announcing a new job before the ethics watchdog could investigate and sanction it. I would urge them to refuse permission for him to take up the role, at least until there is time to properly consider these questions.”

Lewis said he intended to write to the ministerial appointments watchdog to raise the issue and ask it to clarify the timing of Osborne’s application for permission to accept the role.

Friends of Osborne, including his former special adviser Rohan Silva, indicated over the weekend that the former chancellor had applied for the job in early February and accepted a fortnight ago.

The advisory committee on business appointments (Acoba), which considers any conflict of interest in new jobs for former ministers and ex senior civil servants, said it was only contacted last week, just days before the appointment was announced.

Osborne has previously been rebuked by Acoba for announcing his northern powerhouse initiative before seeking the committee’s advice. At the very least, he is likely to be similarly criticised by the watchdog for the timing of the Evening Standard announcement, although it does not have the power to prevent appointments.

One source said it was possible that the committee could still advise Osborne to delay taking up the role, although such guidance would be more difficult given his appointment has already been announced.

“Osborne was already shown the yellow card by the committee for his first offence,” Lewis said. “They have rebuked other officials for this, and there can’t be a double standard. This time they need to get the red card out. The former chancellor has shown total contempt for the rules, so Acoba now needs to show that those rules can and will be enforced.”

Osborne’s decision not to resign as MP for his Cheshire constituency, which is almost 200 miles from London, could prompt an overhaul of rules on second jobs, the chair of the country’s chief standards watchdog has said. Lord Bew, chair of the committee on standards in public life, told the Sunday Times the current rules were “getting into rockier waters”.

“We have not ruled out MPs having second jobs quite deliberately up until now, but we now have to look again at our rules,” he said. “We are going to discuss whether our rules on second jobs need to be changed in light of this.”

George Osborne: I can balance my new editorship with job as MP – video

On Sunday, the leader of the Scottish Conservatives, Ruth Davidson, became the latest senior Tory to say she could not see how Osborne could juggle being a journalist and an MP.

“I spent 10 years as a journalist and I’ve now spent six years as a politician and I’m not sure I could combine them both,” she told the BBC’s Andrew Marr Show. “I work a pretty busy week as it is and ... I’m not sure I could do both at the same time, if I’m honest.”

However, Osborne’s new job was also ex-cabinet minister Nicky Morgan, both prominent remain campaigners who hinted they were pleased someone of his political persuasion was in the post.

Morgan, who co-wrote a piece for the Observer on Sunday opposing grammar schools, said the appointment proved there was still an appetite for liberal conservative voices.

“When you are fired, as we all were last summer, what did the government expect? That we were going to just all disappear?” she told ITV’s Peston on Sunday. “We are going to make our voices heard, whether it’s me writing articles or George being editor. There’s a liberal conservative point of view to be talked about and we are going to do that.”

Evegeny Lebedev, the Russian oligarch’s son who owns the Standard as well as the Independent and the London Live TV channel, took to Twitter over the weekend to deride his new editor’s critics as “sad old commentariat” and said they should wait to see Osborne’s first paper before judging his work.

“Tories saying he will criticise the government now. Labour say he is a Tory stooge. So, which is it?!” he tweeted. “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.”