[joeysteele]

It's not a decided position in Labour.
The party conference is likely to state the actual policy.

If Labour were in government, they'd look to propose a customs union in the agreements.
The EU would support that.
Backstop not relevant anymore.

Then Labour would put their new deal and remain in a referendum.
Leaving voters to either change their minds and remain or take the new deal.

Or, in the absence of a new deal, unlikely
Hold a referendum on no deal or remain.
In that second scenario Labour would support remain.

Emily Thornberry made a mess of trying to outline the options but it's not that hard to understand surely.

The final decision of a new referendum has to be debated and set out at the Party conference in September.