There is cash prize of 100,000 euros (£87,000) for an initial 2,000-word essay giving the best reasons for Britain to leave the European Union.
Former Conservative chancellor Nigel Lawson, who is chairing the Institution of Economic Affairs' panel of judges, spoke of the "fundamental change" of Britain's EU relationship, with the arrival of the euro currency and eurozone.
He reckoned the EU was "not prepared to make any significant changes" and any British prime minister would only achieve "inconsequential" negotiations.
Lord Lawson was speaking with Which? executive director Richard Lloyd and Jo Coburn after they watched interviews with leading politicians on British relations with the EU.