John McDonnell has said Karl Marx and Chancellor Philip Hammond are among those who have influenced his economic thinking.
The shadow chancellor, who was repeatedly pressed on The Andrew Marr Show if he was a Marxist, said there is "a lot to learn from reading Das Kapital" alongside ideas from Labour figures as he bids to ensure the economy is based upon "sound principles and fairness".
Mr McDonnell also rejected claims Labour's tax and spending plans, which include borrowing £250 billion to fund efforts to boost investment in infrastructure and skills, represent a return to the 1970s.
He told the BBC One programme: "Shall I tell you whose advice we took in terms of borrowing? Philip Hammond.
"He said last year we need to borrow for our infrastructure and now is the time to do it.
"We also took the figures from the CBI, the Confederation of British Industry, about how much exactly is needed if we're going to be competitive with our European and American competitors.
"If you look at what (US President Donald Trump) is doing, he's putting a trillion in."
Mr McDonnell was later asked about previously describing himself as a Marxist, including if there was anything to learn from reading Das Kapital.
Asked if he was a Marxist, he replied: "I believe there's a lot to learn from reading Das Kapital, yes, of course it is, and that's been recommended not just by me but many others, mainstream economists as well.
"I also believe in the long tradition of the Labour Party which involves people like GDH Cole, Tawney and others.
"You put that all together and you have, I think, a direction for our economy based upon sound principles and fairness."
Mr McDonnell said "that's where Marx got it wrong" when told Das Kapital predicted capitalism as a system would crash and fail.
He said: "I want to transform the system. That's where Marx got it wrong, we know that."
Mr McDonnell said his transformation idea is based on ensuring prosperity is "shared by all" and "economically sustainable but environmentally sustainable as well".
International Development Secretary Priti Patel said: "The man Jeremy Corbyn wants to make chancellor believes that the nonsensical ideas of Karl Marx – punitive taxes, closing down businesses and the removal of private property – should be at the heart of Britain's economic policy.
"It is just a glimpse of the economic destruction that Jeremy Corbyn and John McDonnell, backed by a coalition of chaos, would unleash on the British economy in less than five weeks' time."