In a significant shift in his position, Mr Ashdown said that if the Prime Minister postponed the poll until the next Parliament for good reasons, "so be it".
Mr Ashdown will have to convince his party that the referendum cannot be held in this Parliament on the Jenkins proposals, which provide for around 80 per cent of MPs to be elected by the alternative vote system, with a 15-20 per cent top-up of MPs elected regionally on a proportional basis.
Mr Ashdown, who negotiated with Mr Blair over the Prime Minister's response to the report, said the Labour Party had a manifesto commitment to holding the referendum. "We have an agreement that it will take place before the next election".
But in a clear concession to Mr Blair, he said he did not want to "close off options". It was right that voters should be able to assess the plans in the context of other far-reaching constitutional reforms, particularly of the House of Lords.
Mr Ashdown confirmed the report in The Independent that he believes Mr Blair is committed to changing the electoral system, and that he will slowly bring the Labour movement toward reform, with his Feng Shui style of leadership, which Mr Ashdown describes privately as "Zen Blairism".
He thought Mr Blair was "emotionally and intellectually" persuaded of the case for reform, and that would pull in an increasing number of Labour MPs behind him.
Jack Straw, Home Secretary, upset Liberal Democrats by hinting that the referendum would be delayed until after the election to take account of the House of Lords' reforms, including possible plans for an elected upper house.
Mr Ashdown signalled that he accepts Mr Straw's argument that the prospect of reform of the Lords has changed the circumstances surrounding the manifesto commitment for a referendum. "If because of reasons beyond our control [the referendum] has to be after the election, then so be it," Mr Ashdown said on BBC1's Breakfast with Frost programme.
The Liberal Democrat leader appeared to join the growing support for a referendum on both issues. A joint poll on voting reform and changes to the House of Lords "has a lot to be said for it",he said.
Mr Ashdown added that the new assemblies in Scotland and Wales, elected using new voting systems, and reforms to the House of Lords had to be given time to settle down and be assessed.
Delaying the referendum would avoid cabinet splits in the run-up to the next election. Mr Ashdown was holding to the view that a referendum in the last year of this Parliament was "probably about right".
Michael Ancram, the Tory party chairman, said he would join a cross-party coalition against the Jenkins proposals. "It will involve businessmen, trade unionists; it will involve journalists.
"It will be a very broad coalition of interest that says the British system might not be perfect, but a least it works - and if it ain't broke, don't fix it."Reuse content