RBS has recently initiated a sale process for all or part of its insurance division, which includes Direct Line and Churchill.
Chief executive, Sir Fred Goodwin, said the insurance arm had already attracted several inquiries. It is thought the sale will raise £4bn.
It has been suggested that some US insurers, including Warren Buffett's Berkshire Hathaway group, which owns US direct insurer Geico and Progressive, a rival US direct insurer might be interested in buying the division.
The insurance division could also appeal to large European insurance groups such as Allianz and Axa. British insurance companies expected to look at the assets include Zurich Financial Services and Aviva.
Direct Line, whose initial service was to sell motor insurance over the phone, was founded by Peter Wood in 1985.
Churchill was set up in 1989 by Martin Long. RBS bought Churchill from Credit Suisse for £1.2bn in 2003.
