JACK McConnell's Holyrood election campaign is in disarray after his chief strategist quit following an internal power struggle.

Steven Lawther, the party's head of communications and spin doctor, has walked out on the job after reported clashes with senior colleagues.

His shock resignation has sparked a last-minute campaign reorganisation and is the latest blow for a Labour campaign marked by internal bickering and turf wars and which has been described by one Labour insider as "the worst campaign I have been involved in for over 20 years".

Lawther, who was hired last year, has quit his highly influential post just weeks before the Holyrood election. It is unclear whether he has a new job lined up.

The official explanation being circulated by the party is that he left for "family reasons", but the Sunday Herald has been told he and senior figures on the campaign clashed over aspects of strategy and presentation.

Lawther, a polling expert, resigned around 10 days ago. His hasty exit coincided with a Labour election campaign U-turn, which saw the party tone down their attacks on independence and instead stress the positive benefits of staying in the union.

Significantly, it was Lawther who was the first to flag up concerns about Labour's difficulties with the voters ahead of the Scottish election.

In a leaked email last year, the spin doctor claimed the party's polling position was "bleak" and "a major concern".

A consequence of Lawther's departure is that it entrenches the grip of the London-based figures who are running Scottish Labour's campaign, notably John McTernan, an aide to the prime minister.

Lawther's resignation has also been followed by more complaints about the Labour team's handling of the election campaign.

One Labour MSP, who used to be a minister, was said to be "furious" that McConnell refused to appear with other Scottish party leaders on Question Time last week, leaving it to Lord Foulkes to face SNP leader Alex Salmond.

One senior Labour insider told the Sunday Herald: "This is the worst campaign I have been involved in for over 20 years. It is appaling."

The gap left in Labour's campaign team by Lawther's exit has been partly filled by Iain Bundred, who has been flown up from south of the Border.

A spokesman for the Labour Party said: "Steven felt this was the right decision for him and his young family: to take a step back from the campaign front line. This is no reflection on his hard work for and dedication to the Labour Party."

SNP leader Alex Salmond said: "There is now every indication that the Labour campaign is disintegrating. As Henry McLeish said, Labour's campaign is London-dominated' and negative'. I think it's reasonable to suppose Mr Lawther agrees with both or one of these facts."