Hmm, prompted by the gransnet competition furore, checked the T and Cs of this and not looking that great but at least there's the option to bow out:
Publication is subject to the winner entering into a contract with Century, an imprint of the Publisher. This will afford an exclusive licence to the Publisher, permitting the editing, adapting, publishing and licencing of all or part of the novel in all editions, formats (including print and electronic), in all languages and territories globally and setting out all applicable financial details including a net advance of £20,000 (the gross figure, before the deduction of the agency commission contemplated below, being £23,000) on completion and acceptance (by Publisher) of the complete manuscript and providing the Publisher with an option over a second book. Should entrants not want to grant these rights they should not submit materials. In the event an agreement cannot be reached, as regards the contract, within 30 days of the discussions commencing, the winner shall instead be awarded the substitute prize.