LABOUR supporters have been warned that if they engage in abusive and intimidatory behaviour, they will be barred from voting in the summer leadership contest.

The declaration by Iain McNicol, the party’s general secretary, came as it emerged that a group of members is suing Labour over its controversial decision to bar some 130,000 people, who have joined it since the January deadline was set by the ruling National Executive Committee.

In a separate development, Sarah Champion, one of a tranche of Labour MPs who quit her frontbench role, saying Jeremy Corbyn’s leadership was no longer tenable, has rejoined his frontline team as shadow home office minister, focusing on women, equality and domestic violence issues.

A spokesman for the leader urged others to follow suit, saying there was “work to be done”. There was no immediate comment from Ms Champion, who represents Rotherham.

In a statement, Mr McNicol denounced the “appalling behaviour” amid recent claims of bullying.

Over the weekend, more than 40 of female Labour MPs signed a letter calling on Mr Corbyn to do more to combat “an extremely worrying trend of escalating abuse and hostility”.

Seema Malhotra, a former shadow Treasury minister, has lodged a formal complaint with Speaker John Bercow, claiming staff working for Mr Corbyn and John McDonnell, the shadow chancellor, entered her office in a serious breach of parliamentary privilege.

Karie Murphy, the Labour leader’s office manager, is said to have entered Ms Malhotra’s Commons office twice when she was not there.

In 2013, Ms Murphy, who is close to Unite chief Len McCluskey, was at the centre of a row over Labour’s selection of an election candidate in Falkirk amid claims of vote-rigging by the trade union, which it strenuously denied.

Mr McNicol told the party that it should be the home of lively debate, of new ideas and of campaigns to change society.

“However, for a fair debate to take place, people must be able to air their views in an atmosphere of respect. They shouldn’t be shouted down, they shouldn’t be intimidated and they shouldn’t be abused, either in meetings or online.

“Put plainly, there is simply too much of it taking place and it needs to stop,” declared the general secretary.

Stressing how Mr Corbyn, his leadership rival Owen Smith, deputy leader Tom Watson and the NEC have all made clear that there was no place for abuse of any kind in the party, Mr McNicol said shortly the party would be taking more action to protect its members and to “identify those responsible for this appalling behaviour”.

He went on: “I want to be clear, if you are a member and you engage in abusive behaviour towards other members it will be investigated and you could be suspended while that investigation is carried out.

“If you are a registered supporter or affiliated supporter and you engage in abusive behaviour you will not get a vote in this leadership election.”

Mr McNicol added: “Choosing our candidate to be the next Labour Prime Minister is a great responsibility on us all. We owe it to the millions of people who need the Labour Party to fight for them, to conduct our Leadership election in a way that gives them confidence in our ability to build a better Britain.”

Meantime, a London law firm has been hired by members and has issued proceedings against Labour and Mr McNicol over the January deadline for eligibility to vote in the leadership contest. The party members, who are seeking to have the matter heard by August 4 in the High Court, are crowdfunding to pay for the action.

A Labour party spokesman said the party would “vigorously defend” the decision by the NEC, which said only members who joined the party before January 12 could take part.

Elsewhere, a poll of Labour councillors in the 250 most marginal parliamentary constituencies showed that 60 per cent were backing Mr Smith for the leadership with 28 per cent preferring Mr Corbyn.

An even higher majority, 65 per cent, thought Mr Smith gave them the best chance of winning their constituency at the next general election compared with 23 per cent who thought it best to stick with Mr Corbyn, the Labour History Research Unit at Anglia Ruskin University found.

Yet despite their preference for Mr Smith, most of the councillors, 38 per cent, believed the majority of local members would vote for Mr Corbyn compared to 28 per cent for Mr Smith and 53 per cent of the councillors thought the majority of locally registered supporters would back the incumbent over just 10 per cent for Mr Smith.