Referendum on voting reform will be held in May

A referendum on whether to change Britain's first-past-the-post electoral system will be held next May, Nick Clegg will announce next week.

The Liberal Democrats secured the promise of an historic public vote as part of their coalition agreement with the Conservatives when the May election resulted in a hung parliament.

Since then, the two parties have been negotiating the timing of the referendum. Mr Clegg has been pressing for an early vote next May to coincide with elections to the Scottish Parliament, Welsh Assembly and English councils. He is anxious to show doubters in his own party that its priorities are reflected in the Government's policies.

A Cabinet committee of ministers from the two coalition parties met yesterday and is believed to have endorsed the 5 May date.

The issue on the ballot paper will be whether to adopt the Australian-style alternative vote (AV), under which people rank candidates in order of preference. The candidate coming last drops out and second preferences are redistributed until one secures more than 50 per cent of the votes. The system is not a form of proportional representation but would ensure that every MP has majority support in their constituency.

The Tories strongly oppose electoral reform and fear they would do worse under AV than first-past-the post. Their MPs will be allowed to campaign for a "No" vote in the referendum.

Although the Liberal Democrats will welcome the May date, Mr Clegg could come under pressure to pull out of the coalition if the public rejects reform.

Labour backed AV at this year's election but its MPs are now divided on the issue. The formation of the Liberal-Conservative coalition has allowed Labour opponents of reform to argue that the coalition partners could combine to freeze Labour out of power under AV. Previously, it was thought the system might encourage anti-Tory tactical voting, with Labour and Liberal Democrat supporters putting the other party's candidate in second place.