Brown warned to tone down his language in clash with Cameron over Scottish elections fiasco

It came after the Prime Minister accused the Tory leader of 'misleading people' about the conclusions of a devastating report into a poll fiasco in Scotland earlier this year.

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That prompted uproar, since it is considered a breach of Commons rules to accuse an opponent of deliberately misleading Parliament.

Proceedings were dramatically brought to a halt as Mr Martin held hushed consultations with the clerks of the House.

As furious Conservative MPs demanded the Prime Minister withdraw the allegation, the Speaker warned Mr Brown: "I call for temperate language."

Mr Cameron called for Labour's election supremo and Mr Brown's close ally, Douglas Alexander, to resign over the independent report into May's elections to the Scottish Parliament and local councils which descended into a shambles that saw more than 140,000 people disenfranchised.

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The report, by Canadian elections expert Ron Gould, concluded that voters had been treated as an 'afterthought'.

Most damagingly, it said ministers were frequently focused on 'partisan political interests' when making arrangements for the elections.

At Prime Minister's Questions, Mr Brown insisted all main parties had to accept responsibility because they all agreed the system that had been adopted.

After he accused Mr Cameron of 'misleading people', a visibly angry Tory leader replied that he did not know how the Prime Minister had the 'gall' to make such a claim.

He quoted the report's conclusion that there was a 'notable level of party self-interest evident in ministerial decision-making'.

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Mr Cameron insisted that Mr Alexander, who was Scottish Secretary at the time and is now International Development Secretary, should 'explain himself to the House of Commons' and be 'stripped of his responsibility for elections'.

"How can he possibly go round the world lecturing other countries about probity in their elections?" Mr Cameron demanded.

The Prime Minister conceded that the Gould report had said 'there were decisions made about the elections that could have been better made'.

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But he insisted: "These decisions were supported by the Conservative Party. What the Gould report does not do is put the blame on any individual or any institution."

The May polls saw a new ballot paper design and a new voting system-for council seats.

Mr Gould found strong evidence that combining both regional and constituency ballot papers on one sheet was to blame for the confusion that meant 146,099 votes having to be rejected because the papers were not filled in properly.

Critics say it was a deliberate attempt to sideline smaller parties such as the Greens and the Scottish Socialist Party.

Voters had traditionally seen the second, separate regional vote as a 'second choice' and a chance to take a risk on a smaller party after their 'main' vote.

Mr Alexander issued a statement apologising for his role in the fiasco.