Culture Secretary Tessa Jowell is also a close ally of Prime Minister Tony Blair. She signed a mortgage document that allowed her husband to move a 350,000 pound ($610,000) bribe to Britain, the Sunday Times of London reported.
Jowell's husband, David Wells, is a corporate lawyer who helped Berlusconi build his business empire. Italian authorities have been investigating Berlusconi for a decade.
Police in London raided Mills' office and the couple's home recently at the request of Italian authorities, the Times said, seizing documents and a computer.
Mills had tried to protect his wife, maintaining that their finances are completely separate. But the mortgage allegedly served as a vehicle for bribery, with an offshore entity repaying the loan after Mills invested the proceeds.