Tony Blair plans to use this as an excuse to shelve Labour's manifesto pledge to hold a referendum on proportional representation - which is being strongly resisted by senior figures in the Cabinet - until the next Parliament.
However, Downing Street sources made clear yesterday that the Prime Minister also intends to give Paddy Ashdown a firm promise that the issue will be put to the people in the lifetime of the next Parliament, in an attempt to retain Liberal Democrat support.
Mr Ashdown, who is coming under increasing pressure from his party over his willingness to compromise, is threatening to end its policy of "constructive opposition" if Mr Blair fails to call a referendum on PR.
The Government will give an ambiguous response when the Jenkins report is published on Thursday. The Home Secretary, Jack Straw, will welcome the work done by the PR Commission and set out plans for a wide-ranging discussion of the issues, including a Commons debate in the next few weeks.
But Mr Blair is expected to delay any announcement on what the Government intends to do about implementing the recommendations.
"We have to be realistic about the balance of opinion in our party and the rest of the country," the Downing Street source said.
Sources close to the PR Commission said that Lord Jenkins would be "disappointed", but members were reconciled to the probability that no referendum would be held in this Parliament.
Lord Jenkins will propose that there should be new "super-MPs", elected to represent a whole county or city, sitting alongside constituency MPs in the Commons.
Under his model, 520-550 MPs would be chosen from larger, redrawn constituencies through the system in which electors express more than one preference and the second choices of weaker candidates are redistributed among the stronger. The remaining 100-130 MPs would be elected as a "top-up" chosen from lists on the basis of the overall share of the vote secured by each party. They would represent larger regions.
Following discussions with Mr Blair and Mr Ashdown, Lord Jenkins has watered down his original proposals by shrinking the size of the "top- up" to make the blueprint more acceptable to opponents of PR.
Although most of the conclusions by the cross-party commission were unanimous, Lord Alexander, the Tory peer, plans to publish a minority report, saying he believes that the constituency MPs should still be elected under the existing first-past-the-post system.
Those campaigning in favour of PR have won the backing of several influential businessmen, including Sir John Harvey-Jones, Lord Haskins and Sir Adrian Cadbury.Reuse content