A Conservative donor has accused David Cameron of an "arrogant, Old Etonian" style of leadership and said he would give the party no more money.
Sir Tom is the founder of the Arriva transport group
Sir Tom Cowie, who has paid £630,000 to the Tories over the past six years, said he had become "disillusioned".
He is now planning to make donations to the Prince's Trust charity instead.
Shadow Foreign Secretary William Hague said when a party was changing "there will always be people who are uncomfortable with that process".
Mr Hague told the BBC: "I think this is a normal part of politics but it should simply spur us on to present our arguments and to continue to drive forward the process of change in the Conservative Party.
"It is essential to do that, that the Conservative Party recaptures the centre ground of British politics."
Sir Tom backed Mr Cameron's 2005 leadership bid but has only donated £25,000 to the Conservative Party since he became leader.
Sir Tom told the Guardian newspaper he was "very, very disappointed" with Mr Cameron and was "disillusioned" with his style of leadership, after what he described as a series of blunders.
He cited the Tory leader's decision to go to Rwanda during the recent flooding in England, which affected Mr Cameron's Witney constituency, and the party row over ending support for grammar schools.
The 84-year-old entrepreneur, who gave more than £500,000 to the party's 2005 general election campaign, said he would not be switching political allegiance to Labour.
In response to a question about the present state of the Conservatives, he said: "Are you sure you don't want to hear foul language?"
He added: "All I can say is I am very, very disappointed with the state of the party.
"I will not mince my words: I shan't send them any more money."
Sir Tom also said: "The Tory party seems to be run now by Old Etonians and they don't seem to understand how other people live.
"They seem to be very arrogant like I suppose Old Etonians can be. They certainly don't understand about grammar schools."
Sir Tom, who took over his father's bicycle repair business in 1948 and built it up into transport firm Arriva, is a former chairman of Sunderland Football Club.
After the 2005 general election defeat, he said the then Tory leader Michael Howard should go "in hours or days".
However, in October 2003 Sir Tom called on party members to stand by Mr Howard's under-fire predecessor Iain Duncan Smith, who was later ousted.
The Conservative Party is in better financial health than its rivals.
Last year, it raised £14.9m in donations, compared with £5.41m for Labour and £5.8m for the Lib Dems.
In February, it made a profit of about £15m on the sale of its former Smith Square headquarters, in Westminster, enabling it to clear most of its debts.
Labour is £26.2m in debt according to the most recent figures filed with the Electoral Commission.