Pressure grew on Gordon Brown to endorse electoral reform last night as union leaders backed changes to the voting system to restore faith in politics.
With senior cabinet members including Alan Johnson, the health secretary, backing the move, signs of left-right consensus emerged as two union leaders added their support.
Billy Hayes, general secretary of the Communication Workers Union and an admirer of Johnson, said it was essential that Brown ordered a debate on electoral reform if he wanted to rekindle faith in the political system.
"We have to have a debate on the issue," he added. "We need to move towards a system in which people can know that their vote counts."
Traditionally, the Labour left has opposed electoral reform, particularly proportional representation, believing it benefits smaller parties at Labour's expense. But with senior figures from the centre-left, including former deputy leader Roy Hattersley, converting to reform, union leaders and leftwing MPs are warming to the idea as a way to get the voice of working people heard.
Last night Mark Serwotka, leader of the Public and Commercial Services union (PCS), also backed change. "It is increasingly clear that there is a democratic deficit in this country. Electoral reform would go some way towards convincing people that their votes count."
The PCS is pushing for electoral reform as part of a "Make Your Vote Count" campaign. Its national conference in Brighton last week passed a motion to consult members on backing pro-public service trade union candidates in elections.
In a letter to the Observer, Alex Salmond, the leader of the Scottish National party, says that the system used at Holyrood would be a model Westminster should copy.
"Holyrood's voting system includes proportional representation, to ensure a more balanced parliament," he says. "That makes it difficult for any one party to achieve an outright majority. And the successful example of minority government which the SNP is now pioneering also breathes new life and meaning into the parliament.
"A key advantage of the Holyrood system is that of fixed four-year parliamentary terms. Following this example at Westminster would go a long way to curbing the power of No 10. No longer would prime ministerial prerogative be able to dictate polling day to try to suit the needs of the incumbent party."
Neal Lawson, chairman of the centre-left pressure group Compass, said a left-right consensus was forming in the party over the need for electoral reform. "There are clear signs that we are reaching a tipping point on electoral reform. The fact that Britain's fourth largest union is now backing it is a sign of the pressure for change."
Johnson has said the government should hold a referendum on electoral reform the same day as the next general election. He said the furore over MPs' expenses demanded a response from politicians: "We need to overhaul the engine, not just clean the upholstery."