JOHN McDonnell, MP for Hayes and Harlington, is the new shadow chancellor.

The new Labour Party leader Jeremy Corbyn announced today his best friend and fellow hard left-winger Mr McDonnell would be in charge of the party’s economic policy.

Mr Corbyn was voted in with a resounding 59.5 per cent in a leadership election on Saturday.

But his decision today to appoint his campaign manager Mr McDonnell has sparked controversy among the party. Some members, including Blair's former home secretary Charles Clarke, have said Labour will not be able to win the next election in 2020 if it lurches left.

Shadow foreign secretary Hilary Benn said only: "I respect the choice that Jeremy has made as leader."

Mr McDonnell, who is strongly anti-austerity, said in July he would “swim through vomit” to oppose the Conservatives’ welfare bill, in defiance of his own party line.

Today the MP, who was chair of finance for Greater London Council in the 1980s, defended his economic credentials.

He said: “I’ve got a long history in terms of financial administration. I was Chancellor of the Exchequer for London at the age of 29. I’ve been in Parliament a long time.

“I’ve not held office because I’ve disagreed with a lot of the New Labour policies, but my new policies with Jeremy’s have been roundly endorsed by the leadership election so, what I’m going to try and do now is make sure we can convince our colleagues in Parliament of the need for change. And that’s within all the political parties, not just the Parliamentary Labour Party, but also convince the public as well.

“The economy is safe in our hands but will also be more prosperous.”

In his blog last month he said he was not in "deficit denial", but he did "not believe the vast majority of middle- and low-income earners who didn’t cause the economic crisis should have to pay for it through cuts in tax credits, pay freezes, and cuts in essential services.

"Instead we believe we can tackle the deficit by halting the tax cuts to the very rich and to corporations, by making sure they pay their taxes, and by investing in the housing and infrastructure a modern country needs to get people back to work in good jobs...

"Our cuts will be to the subsidies paid to landlords milking the housing benefit system, to the £93bn in subsidies to corporations, and to employers exploiting workers with low wages and leaving the rest of us to pick up the tab."

In 2009 the Hayes and Harlington MP was suspended from the House of Commons for five days after angrily grabbing the mace, the ornamental club which represents the royal authority of Parliament, after his party's decision to approve a third runway at Heathrow.