Senior Labour figures were embroiled in the first scandal of the election campaign today after a candidate was sacked for making offensive comments on Twitter.
Stuart MacLennan, 24, was dropped as Labour's candidate for Moray less than four weeks before polling day after details of the remarks emerged.
Opposition politicians challenged senior Labour figures said to have been followers of Mr MacLennan's micro-blog to explain why they had not acted earlier.
The Conservatives and SNP said Ed Balls, Ben Bradshaw and John Prescott had all been followers.
Today, Gordon Brown branded Mr MacLennan's remarks "unacceptable".
The Prime Minister said: "A candidate has made a mistake. It's unacceptable. That candidate has got to resign.
"I have made it absolutely clear what my views are: we cannot have people standing as candidates for the Labour Party who express these views, so that candidate will not be a candidate for the Labour Party."
Mr MacLennan was summoned to Labour's Scottish headquarters in Glasgow this morning where he was sacked.
Labour initially appeared to have rejected calls for him to be dropped. Scottish party leader Iain Gray, who was campaigning alongside Scots Secretary Jim Murphy, stated that while the comments were "absolutely unacceptable", Mr MacLennan had the support of the Labour Party.
However, a short time later it was revealed Mr MacLennan had been sacked.
A party spokesman confirmed he had been axed for "the totally unacceptable language which he has expressed online".
He added: "On reading the comments in full, the Scottish Labour Party was outraged by their content and Scottish Labour's general secretary took the decision to suspend his membership of the Labour Party.
"Stuart MacLennan is no longer a Labour Party candidate nor eligible to hold office as a Labour Party representative."
Mr MacLennan issued a brief statement in which he said: "I am very sorry. I have been stupid and rightly paid a high price."
His Twitter page has now been closed down but the Scottish Sun said he branded House of Commons Speaker John Bercow a "t**", Tory leader Mr Cameron a "t***" and Lib Dem leader Nick Clegg "a b******".
He posted an outburst about veteran Labour MP Diane Abbott, describing her as "a f****** idiot", the paper said.
Mr MacLennan also reportedly called X Factor judge Louis Walsh a "c***", referred to Jedward as "odious little s***s" and wrote: "I f****** hate Paolo Nutini."
Other foul-mouthed messages which he had written later emerged in the course of the day.
Conservative leader David Cameron described the remarks as "pretty appalling" and added: "Jim Murphy, the Secretary of State for Scotland, showed very bad judgment in first of all saying that seemed to be OK.
"If these tweets were sent to other people in the Cabinet, why didn't they do something about it?"
Scottish Tory leader Annabel Goldie said: "What staggers me is senior Labour figures, including Ed Balls, Ben Bradshaw and John Prescott, condoned this behaviour for so long by following his Tweets without protest."
SNP leader and Scottish First Minister Alex Salmond said: "Leading Labour Party figures knew about what he was saying and presumably thought it was all right so long as nobody knew about it."
Mr Salmond stated: "It is now emerging many leading Labour figures, senior politicians, Cabinet members, shadow cabinet members of Scotland, were followers on his Twitter."
He claimed that meant they had known "the sort of things he was saying" but had done "nothing about it".
Mr Salmond added the issue was now "a question of who knew what, when".
He said of Labour: "They stand accused not just of total incompetence and disarray, but of complete and utter hypocrisy."
Meanwhile, Liberal Democrat Scottish spokesman Alistair Carmichael said: "This whole debacle only demonstrates the weakness of Labour in Scotland."
The decision to sack Mr MacLennan leaves members of the local party in Moray searching for a new candidate.
A Scottish Labour spokesman said activists in the area would meet "in the next day or so" to do this and added: "We expect a new candidate to be in place in the next couple of days."