11:43

Unite and Momentum are set to back rival candidates for the battle to become Lewisham East’s next Labour MP, the Guardian has learned.

The development is the latest in an interesting dynamic on the Labour left, first dragged into the open by the battle to become Labour’s next general secretary. Momentum founder Jon Lansman pitched himself against Jennie Formby from Unite, who was backed by the leaders’ office. Lansman eventually withdrew from the race and Formby was selected.

The Guardian understands Momentum’s national co-ordinating group is likely to back Lewisham councillor Sakina Sheikh, a former student campaigner who has close links with the grassroots group. Unite have already formally backed Islington councillor Claudia Webbe, a member of Labour’s national executive committee and a former advisor to Ken Livingstone.

Both candidates have been interviewed by Momentum chiefs to try to win the group’s backing. A Momentum source suggested they wanted to back a candidate with local credentials. “The local Momentum heavily backs Sakina and it feels like she will get the national backing, as they are keen to make sure it’s a local candidate with the endorsement of local members,” the source said.

Unite announced on Tuesday it was backing Webbe, the more experienced candidate, calling her “a lifelong socialist who tirelessly fights the corner of working people, and for justice for those let down by our political system.”

Unite Politics (@UnitePolitics) Unite is proud to be supporting @ClaudiaWebbe to become Labour’s next MP for #LewishamEast. A lifelong socialist who tirelessly fights the corner of working people, and for justice for those let down by our political system. She will be a huge asset in Parliament. https://t.co/0PtAmOSnTU

Two other candidates have also been shortlisted, councillor Brenda Dacres, who stood unsuccessfully to be Lewisham mayor earlier this year, and Janet Daby, Lewisham’s deputy mayor.

Lewisham East’s local party is controlled by party centrists, who are likely to organise for Daby or Dacres other candidates. A Momentum source said the seat could be “a real tough battle” for the left in the local party.