Tensions have erupted over Monday night's TV debate on independence, with the Yes and No camps locked in a furious battle over how many minutes Alistair Darling and Alex Salmond will be given to cross-examine each other.

The politicians themselves were momentarily distracted yesterday when Hollywood actor James McAvoy nominated them to take part in the ice bucket challenge, in which celebrities are doused with freezing cold water to raise money for charity.

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However, behind the scenes a furious row erupted over the format of the BBC showdown. Better Together accused the First Minister's team of trying to dramatically cut the time set aside for interrogation.

That charge was angrily denied by Yes Scotland sources, who described it as categorically untrue.

Both sides remained at loggerheads last night, with the No camp still pushing for the session to be extended and Yes warning that could cut into questions from the audience.

The debate will be broadcast shortly before the first postal ballot papers are sent out.

The No campaign says the BBC initially suggested each leader would be given 10 minutes to cross-examine his opponent, but changed that to six minutes after discussions with Mr Salmond's team.

A Better Together source said: "Presumably it was at Alex Salmond's request because he does not like being cross-examined."

A Yes Scotland source denied a 10-minute session had been suggested. He said the first proposal the campaign received had not included any time for cross-examination, but later the BBC changed that to six minutes and then eight.

He added: "And at no stage did we look for a reduction in the time for cross-examination."

The BBC said the format would be announced nearer broadcast.

* The debate will be streamed live on HeraldScotland on Monday night as part of a comprehensive package of reaction, analysis and comment. Join us here and have your say in our readers' forum.