The Jeremy Corbyn-supporting Momentum organisation has said its membership has reached more than 31,000 as it marks its second birthday.
The group was founded in October 2015 following Mr Corbyn’s victory in the Labour leadership race and has since become highly influential – and controversial – within Labour circles.
Momentum has been credited with mobilising supporters online and on the doorstep during the general election campaign which saw Mr Corbyn’s Labour perform better than many pundits had forecast.
Critics of the group 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 it now has 31,000 activists across 170 local groups, with 15 members of staff.
Jeremy Corbyn speaking at a Momentum event in central London (Rick Findler/PA)
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.”