Fierce divisions within the Labour Party's biggest constituency in Scotland over an MP's reselection have forced its national officials to step in, it was confirmed last night.

The suspension of the 500-member East Lothian constituency's business by the Labour national executive came after what had been described as “poisonous” faction-fighting over the reselection of Anne Moffat, the sitting Labour MP, as the candidate for the next general election. The row is especially embarrassing for Labour in Scotland because East Lothian is the local party of Iain Gray, Labour's leader in the Scottish Parliament. It was being emphasised by party sources last night that the controversy has no connection with Mr Gray.

Party officials in London announced that the business of reselecting a candidate for East Lothian for the next election had been put on ice to allow it to be sorted out by Labour headquarters, possibly next week.

A party spokesman said: “It is normal that the business being transacted by the local party is suspended pending the dispute being resolved. The national executive committee will now work with the local party to resolve matters amicably.”

The row began 18 months ago when Ms Moffat, the MP since 2001, stood for reselection. She was backed by only two of the six local branches, with three others wanting a contest involving other candidates and one branch evenly split. It is understood that the three branches who wanted another candidate were unhappy with Ms Moffat's performance as an MP.

After Ms Moffat was endorsed as a result of votes from trade union affiliates, discontent among local party members grew. Party officials in Scotland investigated the selection process and, it is understood, found that there had been “anomalies”.

The national executive endorsed Ms Moffat's selection and, despite repeated local protests, would not re-open the process. A local source in the anti-Moffat camp said: “It meant that an impasse had been reached but now the national executive has decided to move in to find a way forward. But the question is still there. Does Anne Moffat have the support of local Labour members and the answer is 'no'.”

The move by the national executive does not mean that action has been taken against any of the local officials or that normal local party campaigning has to cease. Ms Moffat declined to comment.

Pro-Moffat campaigners are understood to feel that some members of the local party have acted unconstitutionally by defying the national party.

Ms Moffat has been a relatively low-profile MP but she attracted criticism after claiming £40,000 in travel expenses between 2003 and 2004, more than any other MP. Her defence was that she had to make unscheduled journeys to her constituency to attend to local matters because of a lack of support from local party members.

In May this year, in an unrelated incident, Ms Moffat was mugged by a gang of drunken youths and left with broken ribs while jogging near her home, in Cockenzie, East Lothian. She was knocked unconscious and her watch and jewellery taken by her attackers. She later branded her attackers “scum”.

Mr Gray said last night: "This is a matter for the constituency Labour Party and the Party at a national level. I am pleased that the National Executive committee is seeking to resolve it and I hope that will happen quickly. My work as an MSP continues as usual."

An SNP spokesman said of the affair: “Labour has finally confirmed the worst-kept secret in Scottish politics. Iain Gray is London Labour's man. Since Jim Murphy took over at the Scotland Office Iain Gray will have got used to taking his orders from London - now his constituency party is being run from there too.”

The Scottish Conservatives said: “The people of East Lothian deserve better than this never-ending circus? It is a huge embarrassment for Anne Moffat and indeed Iain Gray.”

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