This week saw the resignation of Heidi Alexander from her very safe seat of Lewisham East, in order to take up the role of London’s Deputy Mayor for Transport. Alexander was formerly the Shadow Secretary of State for Health, before resigning over Jeremy Corbyn’s leadership following the EU Referendum. Her opposition to Corbyn has stunted her role in theParliamentary Labour Party, leaving her on the backbenches while Momentum and other activists apply pressure to her locally.

Alexander’s departure is just the latest in the Labour Party from centrist politicians struggling to find a niche for themselves in Corbyn’s Labour. Sadiq Khan, Andy Burnham, and Dan Jarvis have all carved out roles for themselves in mayoralties, Rachel Reeves found herself a seat as Select Committee chair, and Chuka Umunna is leading anti-Brexit movements in Parliament and out. Not all are so successful of course – most notably Jim Murphy’s brief attempt to lead Scottish Labour ended in ignominy. Front bench seats, previously the most obvious route for ambitious MPs, have rapidly become uncomfortable for those unable or unwilling to commit to Corbynism.

The manner of selecting Alexander’s replacement in Lewisham is also telling. The local Labour Party is accusing the national Party of stitching up theselection to install a Momentum-backed candidate, by centrally imposing candidates and then rushing through the process of shortlisting and selection in just six days. It will be the Corbyn-backed NEC that will choose the by-election candidate.

Corbyn’s ascent in the Party began with the popular support of members. He has since consolidated by taking over the Party apparatus in the NEC and elsewhere. With centrist MPs abandoning the PLP, it is looking increasingly likely that he will soon have a Labour Party made in his own image. Heidi Alexander’s departure brings him one step closer to achieving that.