Britain's high street banks have an institutionalised bias against female-owned businesses, typically charging them one percentage point more in interest on business loans.
Research by Warwick Business School commissioned by the Bank of England also found that banks will lend to minority-owned businesses on more favourable terms than either white male or white female-owned firms.
The research is the first representative survey of SMEs in the UK to offer close analysis of access to external finance for businesses with fewer than 250 employees.
One in five of the SMEs surveyed had a woman as the principal owner. However the report found that the majority female-owned businesses pay significantly higher margins on term loans than male-owned businesses - 2.9 per cent against 1.9 points over base.
At current rates, this means that a female-owned business will typically be paying 7.65 per cent in interest on a loan, compared to 6.65 per cent for a male-owned firm.
This is despite the fact that majority female-owned businesses are more likely to use an accountant and more likely to seek external advice than majority male-owned businesses.
Overall, one in 10 of the 2,500 firms surveyed were refused finance from banks, most because they had no track record, no assets to secure a loan or lacked an acceptable credit history.
Almost one in five also received less money than they wanted.
But there was also bad news in the report for the government's network of small business support schemes such as Business Link. These were found to make no difference to the likely success of raising finance from banks. Having a knowledge of finance and being willing to carry out market research were far more important factors.
According to the Federation of Small Businesses (FSB), who partly funded the research, the findings highlight that SME are continuing to get a raw deal from an industry dominated by the big four banks.
"The serious lack of competition in the small business banking market is a fundamental reason why small firms get a raw deal," said Neil Hamper, FSB Financial Affairs Chairman.
"This report should be a shot in the arm for the banking industry. In 2002 the Competition Commission said the major clearing banks made excessive profits from small businesses and ordered them to undertake measures to promote greater competition.
"This report provides further evidence that small firms, which have £4bn more on deposit with the banks than they owe in loans, still do not receive the service they deserve."
The Warwick report comes only months after research for the Paris-based Forum for Women Entrepreneurs & Executives (FWE) found that venture capitalists in Europe are shunning investments in companies run by women and that there were no more venture capital-backed female businesses in 2004 than there were in 2000.
Female-run firms also received less than 2.5 per cent of the total venture-capital investment in Europe - which was €3.5 billion in 2004.
According to FWE, this huge disparity was partly due to the fact that the male-dominated venture-capital business does not understand the marketplaces women often serve.
But the possibility that SME funding may be affected by similar prejudices was rejected by Joanna Elson, executive director of the British Bankers Association, who said she was "puzzled" by the Warwick findings.
"The truth is we cannot really understand or explain what has happened. One theory is that there are fewer female-owned businesses and they tend to be newer and therefore might be considered riskier."