Seems though that the Remainer MP’s (most of parliament then) are still split as this now:
People's Vote distances itself from new group
A spokesperson for the campaign has sought to quickly distance itself from the pro-EU breakaway group.
“We are not a political party, nor are we ever going to allow ourselves to be associated with just one faction of any political party," they said.
"We are a campaign for a People’s Vote. We are supported by a cross-party group of MPs, as well as by members of the public from all parties and of none.
“Some MPs will have their own reasons for wanting to resign from a particular political party but, as a campaign, we are still working towards securing the support of the Labour front bench."
This is why we will be leaving on 29 March!