Brown makes early overture to Lib Dems

PM to announce constitutional reform package designed to woo Clegg's party in the event of a hung parliament

A far-reaching package of constitutional reforms which could form the basis of a deal between Labour and the Liberal Democrats if the general election results in a hung parliament will be announced by Gordon Brown today.

In a speech this afternoon, Mr Brown is expected to outline his support for fixed-term four-year parliaments, surrendering the Prime Minister's power to choose the date of an election; a "double referendum" on the voting system for Westminster elections; a fully elected House of Lords; and an eventual move to a written constitution.

Mr Brown confirmed yesterday that the election would be held on 6 May. Parliament will be dissolved next Monday and will return on 18 May, almost a week later than usual – which would allow time for negotiations between the parties if none of them wins an overall majority.

Labour still insists that it can win outright because the public mood is so volatile and it stresses that the reforms to be included in its election manifesto next week are designed to rebuild trust after the MPs' expenses controversy – not to curry favour with the Liberal Democrats.

However, the opinion polls suggest that a hung parliament or a Tory win are more likely than a Labour victory, and Mr Brown's reform package will be seen as a way to woo Nick Clegg if the election results in a stalemate. While a formal coalition is unlikely, an understanding in which the Liberal Democrats supported a minority government in key Commons votes is possible. Early legislation on fixed-term parliaments would be a sweetener for Mr Clegg, whose party could be squeezed if a second election were held soon after the first. It could even pave the way for a four-year Lib-Lab pact.

In the heat of battle, the Liberal Democrats will dismiss Mr Brown's "death-bed conversion" to the constitutional change they have long supported. But Labour ministers believe the Brown package could become important if the third party holds the balance of power because the Tories oppose most of the reforms. Although Mr Cameron is attracted by the idea of fixed-term parliaments – already the norm in many other countries – he is not persuaded. He has said that an elected second chamber would not be a top priority. The Tories oppose electoral reform and yesterday blocked the section of a Bill proposing a referendum on replacing the first-past-the-post system with the Australian-style alternative vote method, in which voters rank candidates in order of preference.

On Lords reform, Labour may opt for an 80 per cent elected chamber initially, rising to 100 per cent over time. Church of England bishops are expected to play a continuing role. Today Mr Clegg will attack the record of both main parties on this agenda. The Liberal Democrat leader will say: "If Labour and the Conservatives get their way, only the faces will change. All the corruption and all the sleaze, all the big money and all the backroom dealings will remain. Only the Liberal Democrats can be trusted on political reform. Labour and the Conservatives talk about it. We will make sure that it happens."

In yesterday's opening salvos, Mr Cameron offered voters "hope, optimism, change, a fresh start" in what he called "the most important election for a generation". Promising to seize power for those he called "the great ignored" of Britain, he said: "They want a government that backs them, and that is what the Conservative Party is going to do."

The Tory leader said: "It comes down to this. You don't have to put up with another five years of Gordon Brown."

Addressing a Tory rally in Leeds last night, Mr Cameron said people were "cynical and apathetic and sometimes downright angry with their politicians and I don't blame them." He admitted: "They are not going to give us their support easily ... We have got to earn their support, to show that we are worthy and worth their vote."

The Prime Minister, surrounded by his senior ministers outside Downing Street, did not mention Mr Cameron by name but pointed to their different backgrounds. "I come from an ordinary middle-class family in an ordinary town," he said. His main pitch was on the economy. He asked the people for a "clear and straightforward mandate to continue the urgent and hard work securing the recovery, building our industries for the future, and creating a million skilled jobs over the next five years." He warned that Tory plans to take millions out of the economy this year would put the recovery at risk.

Mr Brown scrapped plans to travel to Washington to attend a nuclear disarmament summit next Monday and Tuesday, which would have allowed him a meeting with President Barack Obama. Downing Street said: "The election campaign has been called and the circumstances have changed." Mr Brown is now expected to launch Labour's manifesto on Monday.

Labour strategists admit the Tories achieved momentum last week by promising to halt next year's 1 per cent rise in national insurance contributions – a decision backed by three more businessmen last night, taking the number to 41. Labour will try to "pick apart" the Tories' claim that the plan could be funded by £6bn of government efficiency savings.

Mr Clegg told party workers at Liberal Democrat headquarters: "This isn't the old politics of a two-horse race between Labour and the Conservative Party. The real choice is between the old politics of Labour and Conservatives and something different, something new, and that is what we offer." Predicting "the beginning of the end for Brown", he said: "This is a huge, huge election."

Today Lord Mandelson, who heads Labour's campaign, will argue that Mr Cameron has failed to transform the Tories despite laying claim to "progressive credentials" when he became party leader.

In a speech to the Labour modernisers' group Progress, he will say Britain must go forward "not with the Labour solutions of the 1970s and not with the Tory solutions of the 80s and 90s but with a new Labour consensus – one that the Tories don't want and do not believe in and one that makes the case for Labour far stronger even than in 1997."