Jeremy Corbyn’s allies have called for Emily Thornberry to resign after she openly challenged his “neutral” Brexit position and said Labour must become the party of Remain.

The shadow foreign secretary yesterday rejected the Labour leader’s official line and said it should be “on the ballot and that Labour campaigns for remain and we lead the campaign for remain”.

In a sign of mounting hostility Len McCluskey, a senior ally of Jeremy Corbyn and general secretary of the Unite union, suggested that Ms Thornberry should “step aside”.

He told Sophy Ridge on Sky News: “My message is to support the leader. When we have a policy on Brexit, and Jeremy Corbyn makes it clear that is the policy, that is what leading members of the