Diane Abbott’s future in the shadow cabinet was in doubt on Saturday night after she failed to guarantee that she would vote to trigger Brexit negotiations in the Commons this week.

The shadow home secretary missed a vote last Wednesday, citing a migraine, after Jeremy Corbyn imposed a three-line whip on his MPs to support a government bill to trigger article 50. Corbyn’s attempts to impose discipline on his MPs had little effect at any level of the party. About 47 Labour MPs voted against the bill at its second reading on Wednesday.

By the weekend, three shadow cabinet members who had joined the rebellion had resigned. Three party whips and 10 other frontbenchers in more junior roles, who had opposed their leader, were waiting to learn whether they would lose their jobs. Most attention was focused on Abbott, a close Corbyn ally. A spokesman for her was unable on Saturday night to confirm that she would definitely back Corbyn, saying only “her office expects her to vote” in line with the whip when she is back. Many Labour MPs from constituencies where there was a strong remain majority in the referendum have refused to back Corbyn, saying they want to reflect the views of their constituents who want to remain and believe Theresa May is leading the country into a hard Brexit that no one voted for.

Abbott’s constituency of Hackney North and Stoke Newington voted by 70% to 30% to remain, according to academic estimates. Labour sources said they expected Corbyn to sack any shadow ministers who rebelled if they had not already resigned. He may be more lenient with more junior frontbenchers and whips, even though the latter are the supposed keepers of discipline. Starting on Monday, Labour will push for cross-party agreement on a series of amendments to try to force the government to agree a “meaningful vote” in parliament on the eventual Brexit deal.

Keir Starmer, Labour’s Brexit spokesman, wants a guarantee that a vote will take place before the agreement is signed off by the EU council and parliament, so there is enough time for it to be improved if MPs reject it. He also wants a guarantee before Brexit talks begin that the more than 2.8 million EU citizens resident in the UK can remain. Labour is not yet clear what its position will be if MPs reject the deal more than once and if no agreement is reached.

Shadow business secretary Clive Lewis has said he will not vote to trigger Brexit at the third reading vote on Wednesday unless a series of amendments is agreed to insure against a hard Brexit. A senior party source said: “If Diane and Clive leave the shadow cabinet over Brexit that will be pretty devastating for Jeremy.”