More than 20,000 people have joined Labour in less than a week after the party prepared for a leadership contest.
According to Jim Pickard of the Financial Times membership has grown by 24,000 in the last week.
It follows calls from Labour figures for those previously members to rejoin to reshape the party and to have a say in the leadership race that will take place before Jeremy Corbyn departs in March.
But with 61% of the 500,000 members backing Jeremy Corbyn at the last leadership election it will need a big shift to move the party away from the continuity candidate.
Meanwhile, pro-Europeans have been urged to join the Liberal Democrats after Labour failed to provide effective opposition to the Tories.
Members of the Lib Dems will also have their say on who should replace Jo Swinson as leader after she lost her seat in the general election.