Reports of Labour rifts over electoral reform in Scottish local government have prompted a fierce attack from the leader of the Scottish nationalists.

It emerged on Sunday that Scottish Labour MPs in Westminster were threatening to push for a review of the electoral system used to elect members of the Holyrood parliament.

Such a move would be seen as retaliation for Jack McConnell's pledge to introduce proportional representation in Scottish council elections.

The first minister agreed to the change as part of a coalition deal with the Scottish Liberal Democrats, but party traditionalists are angered that Labour's grip on key town halls will be weakened.

Commenting on the reports, SNP leader John Swinney said that threats to change the voting system for the Scottish parliament were "anti-democratic".

"This blatantly anti-democratic threat by Labour MPs must be resisted. They have to learn that there is a consensus emerging in Scotland in favour of PR for councils and their threats of retaliation only demonstrate why it is so badly needed," he said.

"This is a classic case of Labour's one party state mentality. They are not arguing that the current system is better for local democracy; their only argument is that it will break the Labour monopoly in council after council."

Swinney claimed the public was fed up with "Labour's municipal cronyism".

"They are tired of their views being ignored and sick fed up of an electoral system that has for too long gifted Labour unadulterated power," he said.

"This is now a major test of Jack McConnell's loyalties and priorities. He has signed up to PR; will he now kow-tow to London Labour, or will he fight for the democratic wishes of the people of Scotland?

"As first minister of Scotland his duty is clear. He must be true to his word an ensure that the 2007 local elections are fought under PR."