Nick Timothy (L) has stated he fears Philip Hammond lacks the policy ideas to overhaul the economy
Nick Timothy, who was one of the Prime Minister's closest aides, accused the Chancellor of lacking policy ideas for overhauling the economy.
He also warned the current leadership at the Treasury risked driving more voters towards Jeremy Corbyn's hard-Left Labour party by failing to have "a burning desire to make people's lives better."
Mr Timothy's broadside, in a newspaper article, increased concerns among Tory MPs that a rift is growing between allies of Mrs May and her Chancellor.
In his article, the former Downing Street adviser wrote: "I fear Philip Hammond's instinct is to maintain existing policy, regardless of its quality.
Philip Hammond has been accused of maintaining existing policy and the status quo
I worry the Chancellor lacks a burning desire to change people's lives for the better, and the imagination to see possibilities beyond how the world works today
"This must not be mistaken for conservatism. Nor is it down to a careful analysis that concludes the status quo is best.
"I worry it is because the Chancellor lacks a burning desire to change people's lives for the better, and the imagination to see possibilities beyond how the world works today."
Mr Timothy, an enthusiastic Brexit supporter, was also damning scathing about Mr Hammond's track record at the Treasury.
He wrote: "In his first Budget, Hammond got it all wrong.
Philip Hammond attended the International Monetary Fund Committee meetings in Washington DC
"Concerned that the rising number of people in self-employment was reducing tax receipts, he increased their National Insurance Contributions.
"Theresa May warned him repeatedly that he was making a mistake, but the Chancellor insisted on going ahead and the inevitable occurred.
"Conservative MPs rebelled and he dropped the policy and the tax receipts that came with it."
Mr Timothy accused the Chancellor of being too focused on balancing the Treasury's books to develop a broader vision of the country's economic future.
He said: "He likes to think of himself as 'Fiscal Phil', the guy who balances the books.
"But the public finances are only one part of the Chancellor's job."
He said Mr Hammond's approach was more suited to the junior role of Chief Secretary to the Treasury rather than the Chancellor's job.
"The Chief Secretary to the Treasury is there to keep spending under control. The Chancellor is supposed to have a wider vision for the country's economy.
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He described the legalisation of same sex marriage as "damaging" for the Conservative Party but also said in time he will come to terms with the change
"With Hammond do we have a Chancellor or two chief secretaries."
Mr Timothy added: "He says he wants to prevent the return of socialism, as proposed by Jeremy Corbyn, but he stops any proposals that would improve economic justice."
During his stint advising the Prime Minister at Number 10, Mr Timothy repeatedly clashed with the Chancellor.
The pair were repeatedly at odds over Brexit.
Mr Timothy quit Downing Street shortly after last summer's snap general election after being blamed by many Tory MPs for the party's much-criticised manifesto.