Party vice-chairman Alan Lewis, 75, was arrested in London yesterday after a woman claimed he raped her in the 1960s in the city of Manchester, north-west England, police said.
Lewis, a self-made tycoon who has earned millions through his luxury clothing chain Crombie, was appointed vice-chairman by Cameron in 2010 and has been honoured by Queen Elizabeth II for his services to British business.
"A 75-year-old man was arrested following a complaint received earlier this year of an historic rape that occurred in the Manchester area in the late 60s," said a spokesman for Greater Manchester Police.
The arrest comes just ahead of the Conservatives' annual party conference in Manchester, which runs from Sunday until next Wednesday.