The former Tory prime minister condemned the conclusions reached in the Jenkins report and defended the existing first-past-the-post system - which saw him ousted and his party suffer a crushing defeat.

In a speech in London, he warned the prime minister: "Be careful over this. Rigging the electoral system would put an indelible stain on government.

"Anyway, we weren't consulted as the Liberal Democrats were, so put aside these private pacts with Paddy."

'Least bad' system

Mr Major also hit at the voting commission's working method, saying they were biased and Conservatives were ignored during consultations.

Speaking on BBC Radio 4's Today programme, the ex-premier admitted the current system was unfair to the Tories at last year's elections.

But it was the "least bad" system he knew. At least it throws up clear governments able to take clear decisions, he said.

The government and the Jenkins Commission had both failed to compare the current system to new ideas, he said.

'Odd but elegant'

Committee members were appointed by ministers who knew they were opposed to the current system and were excluded from comparing new options with first-past-the-post, Mr Major told Today.

"They then consulted among themselves, consulted the leader of the Liberal Democrats, consulted the prime minister and ignored William Hague. I think it's an odd way to proceed."

The report was elegantly written, Mr Major - still the MP for Huntingdon - conceded, but did not make a satisfactory case for change.

He admitted the present system was "a little unfair" to Tories last time.

But he went on: "The fact that it is occasionally unfair to governments or even oppositions is a lesser problem than having a system that may mean a government is formed by deals after the ballot boxes have closed with the government determined by whatever backstairs deal it might do with a third party or even a fourth party or fifth party. I don't think that makes for stable government."

Under the AV Top-up system suggested by Lord Jenkins, government would be institutionally weak, usually coalition, and unable to make decisions, Mr Major said. A party would only be kept in power if it kept the goodwill of a minority party.

Many Labour MPs shared his reservations and he believed they would win a No vote in a referendum, he said.