I may be proven wrong on this - although people have been claiming on twitter for the last few weeks that member numbers are up - but I find it hard to believe.
When Tony Blair became leader of the party there was no huge influx of members, in fact after the Iraq war membership dropped from around 250,000 to 190,000. However, When Corbyn took over the leadership, the membership numbers quickly swelled to upwards of 550,000, the largest in Europe. Obviously this accounts for far more than the return of members who left due to the invasion, and I was one of these. No, so many people rushed to join the party because they were politically homeless and saw an opportunity for a different kind of politics. They were excited for change. Hence why the numbers didn't swell significantly during the Brown/Miliband tenures. It is excitement for change, from the politically homeless that causes large influxes of new and returning members. So you have to ask, what has inspired so many people in this passage from Miliband to Starmer to rush to join the party in such great numbers; greater than those who are leaving due to the treatment of Corbyn? And why did Blair himself, who i regard as a much better, more inspiring performer than Starmer, not enjoy the same groundswell of support right after the Thatcher/Major years?