Labour's 1997 election manifesto promised a public vote on PR for Westminster during this Parliament.
However, senior party sources said that Mr Blair had "little enthusiasm" for the idea since the elections to the European Parliament and Scottish and Welsh assemblies, which were fought on PR.
Opponents are now stepping up their battle to retain the first-past- the-post system by calling for Labour to drop the commitment for a PR plebiscite from its manifesto at the next general election.
Liberal Democrat leaders are increasingly gloomy over the prospects of a referendum in the next Parliament.
The turning point came after Labour was forced to haggle with the Liberal Democrats over tuition fees, in spite of winning the highest number of seats, because Liberal Democrats hold the balance of power in the Scots Parliament.
At a recent meeting in which Mr Blair discussed the PR system in Scotland and Wales, he asked pointedly: "Whose idea was this?"
William Hague, the Tory leader, who is strongly opposed to PR, taunted Mr Blair yesterday at Prime Minister's Question Time. "Why doesn't he stick to his manifesto?" said Mr Hague.
Mr Blair replied: "No, the system that is proposed [by the Jenkins Commission last October] couldn't be introduced in time for the next election."
Downing Street later signalled that a referendum would not be held before the next election. "We are keen that there is a wide debate, not only in Parliament and the political parties but also across the country," it said.
Last night Mr Blair tried to calm the jitters among Labour MPs over the party's unexpected Euro election defeat when he met backbench leaders at Westminster.
He told them: "I am confident we will have a powerful platform to take back to the British people [at the general election]. We will be facing a Tory party we can rightly describe as extreme."
Concern over Labour's performance surfaced at the weekly meeting of the Parliamentary Labour Party, when MPs expressed anxiety at the failure to mobilise supporters in its traditional heartlands. There were demands for more government action to help poor people, particularly pensioners.Reuse content