"Tony Blair has undermined his own claims to be dealing with the foot-and-mouth disease by devoting time to another shabby deal to buy off Charles Kennedy on PR," he said in a statement.
A review would be a watering-down of Labour's unfulfilled 1997 manifesto pledge to hold a referendum on electoral reform, but pro-reformers had feared the party would drop any reference to the subject at the coming election.
Cabinet Office Minister Lord Falconer told the BBC: "The promise given is that we will review how the various systems of election are going in the Scottish Parliament, the European Parliament, the Welsh and London assemblies.
"If that review recommends that there should be a change then there will be a referendum, but before you get to that stage you have got to review how the existing systems are going and that seems only sensible."
Mr Kennedy has indicated he views the latest Labour commitment as progress for the cause of proportional representation (PR).
'Inevitable process of renewal'
In a statement he said: "The Labour Party's manifesto commitment makes clear that the case and the cause of constitutional reform, particularly fair votes, proceeds.
"Westminster cannot remain hermetically sealed much longer from this inevitable process of renewal."
Paddy Ashdown, Mr Kennedy's predecessor as Lib Dem leader, said that the deal was "a very sensible outcome".
Conservative party chairman Michael Ancram accused Mr Blair of neglecting the foot-and-mouth crisis in order to strike a deal with Mr Kennedy.
"Tony Blair has undermined his own claims to be dealing with the
foot-and-mouth disease by devoting time to another shabby deal to buy off
Charles Kennedy on PR," he said in a statement.
Review in 2003
According to Labour sources, the manifesto will state that "the government has introduced major innovations in electoral systems used in the United Kingdom for the Scottish and European parliaments and the Welsh and London assemblies".
"We will review the experience of the new systems and the Jenkins report to assess whether changes might be made to the electoral system for the House of Commons.
"A referendum remains the right way to agree any change for Westminster."
Officials said that the review will be carried out after the summer of 2003 when the next elections in Scotland and Wales are due to be held.
Jenkins report shelved
The Jenkins report was a result of a commission into the issue of electoral reform chaired by Liberal Democrat peer Lord Jenkins of Hillhead.
Labour had promised to have a referendum on the issue in its last manifesto and the matter has been seen by Lib Dems and Labour pro-reformers as unfinished business.
Pressed on why the last manifesto pledged to hold a referendum without mentioning any review, Lord Falconer said: "In the 1997 manifesto we said we'd set up the Jenkins Commission ,which we did ... the Jenkins Commission couldn't be implemented before any election."
He said the "obvious right" course was to launch a formal review but he denied it was just a sop to the Liberal Democrats.
"No, we're not stringing them along - that's an incredibly cynical view."
'Weasel words'
Liberal Democrat foreign affairs spokesman Menzies Campbell insisted that the "march towards proportional representation continues and Charlie Kennedy is well entitled to be satisfied with that outcome".
He said it was "only sensible" to learn the lessons from the elections, where PR was already operating.
But other Lib Dems were more sceptical about the prime minister's motives.
Donnaichadh McCarthy, a member of the party's national executive, told BBC News: "That wording by Blair in the manifesto looks like weasel words."
He described the new pledge as a "very weak commitment" and said there was no deal as Mr Kennedy had given nothing in return.