Although claims in a Sunday newspaper that Mr Blair was about to adopt the change were dismissed by all concerned, a spokeswoman said the No 10 policy unit had looked at the "alternative vote" (AV) system. Ministers have already confirmed that an electoral commission to be announced this month will consider it along with other options.
Under the AV system, voters write down their first, second and third choices of candidate. Second and third choices are then reallocated until one candidate has more than 50 per cent of the vote.
If the Government does decide on this system, the decision would be highly controversial. Labour's manifesto promises "a proportional alternative" to first-past-the-post voting, and Mr Blair is on record as saying AV is not a proportional system.
One study has suggested that if this year's 1 May election had taken place under AV, Labour would have won 452 seats instead of 418, the Liberal Democrats 90 instead of 46 and the Conservatives just 88 instead of 165.
The Liberal Democrats, who will have seats on the new electoral commission, would be very much against this system. They say they want election results to give a truer reflection of the way people vote. The party's leader, Paddy Ashdown, described yesterday's rumours as "kite-flying", possibly by a member of the Cabinet. Interviewed on breakfast television, he said he would be "amazed" if Mr Blair had really made up his mind before the commission was even appointed. "I may relish the fact that the Conservatives would be damaged by this, but I want a system for the country which is fair," he said.
A Downing Street spokeswoman said Mr Blair was still "not persuaded" of the case for proportional representation (PR), despite the manifesto commitment.
The AV system would also be controversial within the Labour Party. Although Jack Straw, the Home Secretary, has said that if there were to be voting reform he would prefer this kind, others who favour PR are not convinced. Many would prefer the system being introduced for the Scottish and Welsh parliaments, with members elected through first-past- the-post sitting alongside a smaller number selected proportionally from party lists.
- Fran Abrams