Tessa Jowell, the Culture and Media Secretary, today categorically denied harbouring any "guilty secrets" after becoming drawn into an investigation into business dealings between her husband and the Italian Prime Minister

The Conservatives have called for an inquiry after The Sunday Times reported that Ms Jowell had signed an application to raise about £400,000 by remortgaging the London home she owns jointly with her husband David Mills.

The loan was repaid within weeks but, in a complex series of financial transactions, was allegedly used by her husband to gain access to a £350,000 long-term loan or gift that Italian prosecutors say was paid to him by Silvio Berlusconi for help in two corruption hearings.

Mr Mills has denied lying at the court hearings in 1997 and 1998. Italian authorities will decide by March 7 whether to press charges which carry a three-year prison sentence.

Meanwhile in Westminster, the escalating scrutiny overshadowed the launch of a report by Ms Jowell's department identifying that women on average earn 17 per cent less than men.

During media interviews to launch the report, the Culture Secretary - who has hitherto entirely distanced herself from the saga - was questioned instead over the extent to which she was aware of her husband's financial affairs. She mounted a stern defence, repeatedly insisting that she had done nothing wrong.

Mrs Jowell also stated that the money used to repay the loan raised against their £700,000 home had "categorically" not come from Signor Berlusconi.

She told Woman's Hour on Radio 4: "If I felt I or my husband were harbouring some guilty secret, I would be very worried indeed. This is a very tough time. It would be a hell of a lot tougher if I felt that I had done something wrong."

Ms Jowell told the BBC that her husband, a lawyer who specialises in tax avoidance schemes, dealt with mortgage repayments and she had been happy to sign the application.

"What I did was sign a form that enable the bank to take a charge on our house in order my husband could buy some investment he wanted. Both of our houses are in our joint names - it's as simple as that," she said.

"I was perfectly happy in the division of our finances to sign the charge," she said. "It simply wasn’t a problem. It wasn’t unusual, it wasn’t improper and it certainly wasn’t illegal."

The Conservatives have formally asked Sir Gus O’Donnell, the Cabinet Secretary, to investigate whether Ms Jowell had breached the ministerial code.

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