Centrist Labour MP Heidi Alexander has announced she is quitting parliament to accept a job working for Sadiq Khan.
Alexander, the MP for Lewisham East since 2010, served as the London mayor’s campaign chair in the 2016 mayoral race.
She will become deputy London mayor for transport. The move will trigger a by-election in her parliamentary seat.
Alexander, a fiercely pro-EU campaigner, said she wanted to help make London’s transport network the “envy of the world”.
And in a letter to her local Labour Party members, Alexander said she was “very sorry” for not having told them sooner about her decision to quit.
Khan said: “Heidi is respected across the political divide as a parliamentarian and campaigner, and Londoners can be confident she will ensure we deliver our ambitious plans to transform London’s transport network over the coming years,” he said.
Alexander served as Jeremy Corbyn’s first shadow health secretary, but quit the frontbench in June 2016 ahead of the second leadership challenge and branded the shadow cabinet “entirely dysfunctional”.
Corbyn thanked Alexander for her “service to the people of Lewisham”.
“I wish Heidi well in her new role as deputy mayor for London in Sadiq Khan’s team, where I know she will put her talents and knowledge to great use for the people of London,” he said?
Alexander has been a fiercely pro-EU voice on the Labour backbenches and has lobbied for the UK to remain in the European Economic Area (EEA) after Brexit.
Sshe held Lewisham East at the snap 2017 general election with a clunking majority of 21,123 votes and Labour will be confident of retaining it.
However the fight to become Labour’s candidate in a seat with a big leftwing Momentum presence could be more intense.
One local councillor Sakina Sheik has already announced her intention to seek the seat.
“The Labour Party is undergoing a transformation led by the grassroots activists and I am proud to be part of this movement,” she said in a statement.
“Jeremy Corbyn has opened the door to a new kind of Labour Party, one which stick to its principles, opposes neoliberalism and utilises the knowledge and experience of its members.”
Alexander, who has been targeted by the left of the party, told Labour activists in Lewisham: “I will of course continue to support the Labour Party and Lewisham will remain my home for many years to come.
“Thank you so much for all the support you have shown me. Lewisham East Labour Party is a product of its brilliant members. I have been so proud to be your representative.
“It is a job I could not have done on my own. Politics works best when it is a team sport. My staff have been second to none and I thank them from the bottom of my heart - the successes were all theirs and the mistakes all mine.
“Please keep in touch. I hope you will understand the reasons for my decision, even if you do not agree with it and I thank you once again for giving me the opportunity to serve - it has been a genuine privilege.”