Charles Kennedy has accused Tony Blair of failing the electorate by refusing to hold a "serious debate" about proportional representation, as he stepped up pressure on the Government to reform the voting system.

The Liberal Democrat leader said the level of public support for voting reform, "reignited" by The Independent's Campaign for Democracy, deserved "a proper public response" from Mr Blair.

In a strongly worded personal letter to the Prime Minister, Mr Kennedy called on him to begin "constructive" talks about the voting system with the Liberal Democrats.

He accused Mr Blair of having "courted" Paddy Ashdown "with promises of reform of the voting system and a switch to proportional representation," which he had not kept.

"In government, you set up a commission under the late Roy Jenkins - then refused to implement its findings," he added.

He told the Prime Minister: "You have failed the electorate over the issue of PR," arguing there is an "overwhelming case for electoral reform".

Mr Kennedy called on Tony Blair to make "a prime ministerial statement about your personal position on electoral reform and your Government's intentions. There should be no equivocation and a clear vision. Surely, the time has come to listen and to engage with the nations of the UK."

Today, Liberal Democrat and Labour peers will apply more pressure on Tony Blair to conduct a public review on PR for the Westminster elections during a debate in the House of Lords. During a special debate on the electoral system, they will seize on the fact that Labour's majority of 67 seats was delivered with a majority of just 36 per cent of the national vote.

Lord Lipsey, the Labour peer who is leading the debate, will question the Government's legitimacy and its mandate to govern. He will warn that "either our electoral system is re-examined or our democracy will rot."

"I should have thought that an electoral system with any claim to be democratic has to pass one minimal test. That is to say, the rules of the game have to be such that parties that do equally well in votes should do equally well in seats," he will say. "The British electoral system no longer meets that test. Indeed now it fits more readily into the various corruptions of democracy seen round the world, where gerrymandering is employed to keep those in power, in power."

On Tuesday, the Prime Minister sent a strong signal that he would not countenance electoral reform when he put the Deputy Prime Minister, John Prescott, who is vehemently opposed to PR for the Westminster elections, in charge of the cabinet committee on electoral reform. Mr Prescott replaced Peter Hain, who is in favour of reforming the voting system, as chairman of the cabinet committee responsible for electoral issues. That move was sharply criticised by Mr Kennedy yesterday. He said it was like "putting King Herod in charge of a maternity ward".

"I don't suppose that John Prescott's views about PR are going to change very much, but then there hasn't been much in the way of indication thus far from the Government that they are rethinking their approach," he said on BBC Radio 4's Today programme.

The Independent's campaign for democracy is gaining fresh momentum with support from across Britain and all sections of the population. Thousands of people have now signed a petition calling for a review of the voting system, while thousands of others have sent in a coupon addressed to Tony Blair calling for urgent reform.

This week leading voting reformers met to discuss how to build on public support for electoral reform.

"There is a growing public dismay about the way the voting system is distorting democracy in Britain and the Prime Minister will not be able to ignore this for much longer," said Nina Temple, the director of Make Votes Count. "All the signs are that the Prime Minister is deaf to these cries of public concern, but he should rediscover his old reforming spirit and help to drive forward the modernisation of Britain's democracy."