Membership for the Jeremy Corbyn-supporting group Momentum has seen its membership swell to more than 30,000, just two years after it was formed.

The campaign organisation started after Mr Corbyn's victory in the Labour leadership race in 2015 and has become highly influential - and controversial - within Labour circles.

The Labour leader had been under pressure to step down as polls showed the party’s popularity at rock bottom, while senior figures also said it would bomb in a general election under his watch.

But Mr Corybn fought off the leadership battle and the party gained ground in the following election – much of it credited to Momentum’s social media campaigning and doorstep canvassing.

Critics of the group, however, claim its activists have taken over constituency Labour parties and agitated against sitting MPs who are critical of the leader.

Momentum said it has added 1,500 new members since Labour's conference in September and that it now has 31,000 activists across 170 local groups, with 15 members of staff.

Co-founder Adam Klug said: "Over the last two years Momentum has become one of the most significant organisations in British politics.

"Our members have breathed life into the Labour Party by getting involved at a local level, running educational events, getting out into the community and supporting workers' struggles across the country.

"The same can't be said for the Tories. The lifeless, moribund Conservative Party on show in Manchester last week was a good example of what happens when a party doesn't empower its members. The intellectual energy disappears, a lack of vision sets in and members begin to desert the party.

"Conservatives should be embarrassed they only have 100,000 members, and we're committed to making sure that ordinary people from across the country continue to join Labour and get involved in their local Labour parties."

Labour Conference 2017 – in pictures Show all 14 1 /14 Labour Conference 2017 – in pictures Labour Conference 2017 – in pictures Britain's opposition Labour Party Leader Jeremy Corbyn delivers his keynote speech at the Labour Party Conference in Brighton Reuters/Toby Melville Labour Conference 2017 – in pictures Senior members of Britain's opposition Labour Party listen to Leader Jeremy Corbyn deliver his keynote speech at the Labour Party Conference in Brighton Reuters/Peter Nicholls Labour Conference 2017 – in pictures Diane Abbott receives a standing ovation during Jeremy Corbyn's speech at the Labour Party conference BBC Labour Conference 2017 – in pictures Labour Leader Jeremy Corbyn addresses delegates on the final day of the Labour Party conference on September 27, 2017 in Brighton Leon Neal/Getty Images Labour Conference 2017 – in pictures Labour Leader Jeremy Corbyn stands with Shadow Secretary of State for Business, Energy and Industrial Strategy Rebecca Long-Bailey (left) and Shadow Secretary of State for Education, Angela Raynor after speeches in the main hall, on day three of the annual Labour Party Conference on September 26, 2017 in Brighton Getty Labour Conference 2017 – in pictures Angela Rayner, Shadow Education Secretary, addressing the Labour Party annual conference at the Brighton Centre, Brighton PA Labour Conference 2017 – in pictures The mayor of London Sadiq Khan delivers a speech at the Labour Party Conference in Brighton, Britain Reuters Labour Conference 2017 – in pictures Dennis Skinner addressing the Labour Party annual conference at the Brighton Centre, Brighton PA Labour Conference 2017 – in pictures John McDonnell MP, Shadow Chancellor of the Exchequer Labour Party Conference, Day 2, Brighton Rex Labour Conference 2017 – in pictures Shadow Chancellor of the Exchequer John McDonnell (C) speaks with Labour party's leader Jeremy Corbyn (L) ahead of making a speech on the second day of the Labour Party Conference AFP/Getty Images Labour Conference 2017 – in pictures Labour Leader Jeremy Corbyn addresses supporters during a momentum rally on the first day of the Labour Party conference Getty Labour Conference 2017 – in pictures Jeremy Corbyn listens to speeches in the main hall on the first day of the Labour Party conference Getty Images Labour Conference 2017 – in pictures Labour Shadow Home Secretary Diane Abbott addresses delegates in the main hall on the first day of the Labour Party conference on September 24 Getty Labour Conference 2017 – in pictures Jeremy Corbyn addresses a rally ahead of the Labour Party Conference in Brighton Reuters

It came as a surprise poll found that voters preferred Mr Corbyn as the next prime minister over Theresa May, according to an exclusive survey for The Independent by BMG Research.