Local council elections
British Labour Party leader Jeremy Corbyn is facing mounting pressure by his own MPs and peers to back a bid to keep the UK in the single market after Brexit.
The Labour party hierarchy is being accused of "cowardice" for telling peers not to support a call for the government to negotiate a Norway-style Brexit within the European Economic Area (EEA).
Former shadow cabinet minister Chuka Umunna says it would "go against Labour's progressive values" not to back the move in Parliament on Tuesday.
But shadow international trade secretary Barry Gardiner says such an arrangement would reduce the UK to being a "rule taker" without a seat at the table when decisions on regulations are made.
Shadow chancellor John McDonnell insists the party must compromise to balance the interests of Leave and Remain voters.
Pro-EU Labour parliamentarians have reacted with fury over the party's refusal to support Lords amendments which would require the government to negotiate EEA membership.
Mr Umunna, a supporter of the pro-EU Open Britain campaign, said staying in the single market was "important in avoiding a return to a hard border" between Northern Ireland and the Republic of Ireland.
"Given the numbers of Conservative MPs now supporting the UK continuing to participate in the EEA, Labour is looking a gift horse in the mouth.
"We can keep the UK in the EEA - and its protections for workers, consumers and the environment - by supporting this move.
"We know the damage leaving the single market will do to our economy, to public services and to our NHS, so it would go against Labour's progressive values for the party not to vote in favour of these amendments tabled by Lord Alli, a leading equalities campaigner, in the Lords."
Alison McGovern, co-chair of the Labour Campaign for the Single Market, said: "The Government's own analysis shows that crashing out of the single market will cause a crippling hit to our economy, which is why it made no sense for Theresa May to rule out single market membership before the Brexit negotiations had even started."
Labour's Lord Alli, one of the signatories to the amendment, accused Labour leadership of "complete cowardice" by ordering peers to abstain.