The leaders of the newly formed Labour movement Momentum say it is ready to defend Jeremy Corbyn should he face a leadership challenge in the aftermath of the May elections.

Momentum has an estimated 90,000-100,000 supporters, and its leaders also say they will use their volunteer base to try to make a difference in marginal council seats and avoid a poor Labour showing that could ignite a challenge to Corbyn in the first place.

Jon Lansman, one of Corbyn’s closest advisers and a driving force behind Momentum, said: “We campaigned to elect him and we will most certainly defend him and support him if there is a challenge. We absolutely have the machinery to run another leadership campaign if we have to and we are absolutely equipped to do that. And we will if necessary and I am confident we will win it.”

Momentum aims to turn itself into a mass social movement similar to other community-based political groups in Europe, but the organisation is viewed with suspicion and outright hostility by many in the parliamentary Labour party (PLP). Many of these MPs are wary of its support and fearful it might yet be used against them in selection contests resulting from proposed boundary changes.

Corbyn’s camp, meanwhile, is worried that his opponents in the parliamentary party are setting a high bar for success in the elections due in Scotland, for local councils in England and in London. To trigger a leadership contest in the aftermath would require 51 Labour MPs and MEPs.

There is an unresolved standoff over whether Corbyn could automatically stand again. Opponents said he would have to secure the support of a quota of MPs, which he might struggle to get. An alternative way to try to unseat him would be to hold a vote of no confidence, but this would require a majority of the PLP, 116, which might prove harder to achieve.

His allies are so nervous that he could face a leadership challenge they are proposing a series of changes to party rules to ensure he is guaranteed a place on the ballot paper. The draft proposals by the Campaign for Labour Party Democracy would lower the nomination threshold in a leadership contest from 15% of Labour MPs and MEPs to 5%.

Lansman, who was elected to Momentum’s 14-strong national steering committee in February, said: “I have to say there are some people in the party who are more interested in creating an opportunity to challenge Jeremy than to win in May and I very much regret that.

“I very much regret that they do not not seem to care about creating an appearance of disunity which does damage to the party. Having spent much of the last 30 years being lectured about the need to support the leadership, I find it incredible that those that the did the lecturing now seem to have so completely changed their minds.”

Jeremy Corbyn and his team hope to turn Momentum into a mass social movement.

At a meeting of the parliamentary Labour party on Monday night, Corbyn attempted to face down his critics, calling for an end to “back-biting, public attacks and constant sniping”. But there was little sign he succeeded in quelling the potential revolt. In the increasingly febrile atmosphere, the Barnsley Central MP Dan Jarvis is still being touted as a potential leadership challenger.

Corbyn and his team are ambitious about Momentum, hoping to turn it into a mass movement, mainly of the Labour party but with part of its footprint outside to attract new supporters.

But it has proved controversial. The Labour MP for Barnsley East, Michael Dugher, who Corbyn sacked from his post as shadow culture secretary, called it a “mob”; his office told the Guardian he had not withdrawn the remark.

Labour’s deputy leader, Tom Watson, described it as a “rabble”, though he has since partially revised that judgment. He said: “When I used the phrase, it was because in the early weeks after they were founded, they seemed very disorganised and often there were different groups making contradictory claims about their purpose. Now that Jon has stamped his authority on the organisation, they seem to have a more consistent programme of activity and a lot of people will reserve judgment on how their programme will play out in the life of the Labour party.”

Momentum provided glimpses of its potential in December when it sent five busloads of volunteers supported by £5,000 raised through crowdsourcing to the Oldham West and Royton byelection, where Labour had been predicted to do badly. Labour not only held the seat but increased its share of the vote from the general election.

It also mobilised in support of Corbyn’s line against the bombing of Syria before a Commons vote, also in December, lobbying Labour MPs.

Labour’s election director, Patrick Heneghan, has told the shadow cabinet to brace itself for damaging setbacks in the May elections. In 2012, Labour gained more than 800 council seats.

Corbyn supporters fear his opponents are trying to set an ambitious target of gaining about 400 seats, which could prove near-impossible to achieve given that 2012 was a high-water mark.

To try to minimise losses, Momentum volunteers could be sent into marginal seats. Turnout is often low – only 32% in 2012 – and victories can turn on relatively few votes.

Lansman said: “We will be targeting the places where we can make the biggest difference. We are going to get all the people out in place where it will make a difference. We want Labour to win and we want Jeremy to win. It will help consolidate Jeremy’s position but it will increase Labour’s representation.”

Corbyn has control of most of the party’s power bases – the leader’s office, many of the unions, the bulk of constituency party members and Momentum – but can count on only a small proportion of the PLP’s 230 MPs.

The Labour leader spends much of the week travelling around the country, buttressing support.