Karl Marx has “come back into fashion,” newly appointed Shadow Chancellor John McDonnell has said, after winning the support of French left-wing economist Thomas Piketty.

McDonnell told the BBC on Sunday that the 19th century socialist revolutionary thinker was a “definitive analyst” of the capitalist system, even though many “might disagree with his conclusions.”

He added that Marx’s seminal work, “Capital,” is essential reading for anyone trying to understand the capitalist system.

Labour leader Jeremy Corbyn’s appointment of McDonnell as shadow chancellor ruffled feathers in the party’s parliamentary ranks, with some MPs believing his economic beliefs are not centrist enough to win a general election.

During his first speech at the Labour party conference in Brighton, McDonnell pledged to launch "aggressive" measures on large tax-dodging corporations like Starbucks and Amazon.

“We are embarking on the immense task of changing the economic discourse in this country. We are throwing off that ridiculous charge that we are deficit deniers,” he said.

“We are saying, tackling the deficit is important but we are rejecting austerity as the means to do it. We are setting out an alternative based upon dynamically growing our economy, ending the tax cuts for the rich and addressing the scourge of tax evasion and avoidance.”

Labour Party Conference: Jeremy Corbyn runs gauntlet http://t.co/TEyw9AmTe6pic.twitter.com/DdmmJD6myY — RT UK (@RTUKnews) September 25, 2015

Asked about Marx on BBC Radio 5 Live, McDonnell said: “If you look at our capitalist system, one of the definitive analysts of how it works – not whether it is condemned, or whether it is right or wrong, just the mechanics of how it works, when it was first formed and how it would be developed – actually was Marx.

“If you look at most of the institutions that are teaching economics today, Marx has come back into fashion because people have gone back to his analysis of just the basics of how the system works.

“People might disagree with his conclusions about what to do with the system, but actually to understand how the system works he comes up with some interesting analyses that have been built in to traditional and fairly classical economics.”

His remarks come after celebrated French economist Thomas Piketty accepted a role in Labour’s new economic advisory committee.

The professor, who won global recognition for his international bestseller, “Capital in the 21st Century,” will “discuss and develop ideas” around the party’s economic policies and strategy.

“I am very happy to take part in this economic advisory committee and assist the Labour Party in constructing an economic policy that helps tackle some of the biggest issues facing people in the UK,” Piketty said.

“There is now a brilliant opportunity for the Labour Party to construct a fresh and new political economy which will expose austerity for the failure it has been in the UK and Europe.”

The newly appointed committee will also include, amongst others, Nobel prize winning economist Joseph Stiglitz and professors Ann Pettiffor and Simon Wren-Lewis.

Corbyn said the group would deliver his "economic vision".

“I was elected on a clear mandate to oppose austerity and to set out an economic strategy based on investment in skills, jobs and infrastructure. Our economy must deliver security for all, not just riches for a few.

“I am delighted that John McDonnell as Shadow Chancellor has convened this group to advise the leadership as we set out our economic vision.”

However, “Corbynomics” as it has been dubbed, has been criticized by former City watchdog Lord Turner, who said voters may not be swung by the veteran left-winger’s policies.

Turner, who chaired the Financial Services Authority (FSA) during the 2008 financial crisis, questioned Corbyn’s policy of people’s quantitative easing.

“The legitimate concern is that if monetary finance is proposed by people who come from a strongly socialist tradition – a tradition that has tended to reject the idea of any disciplines on public expenditure – there is a danger in practice that it would be used to excess. That is the concern which Corbyn would have to address,” he warned Monday.