Jeremy Corbyn has come under increased pressure over his stance on the EU referendum after one of his shadow ministers pledged to quit the front-bench if he decides to campaign for a Brexit.
Lord Falconer, who became one of the first members of Mr Corbyn's front-bench team as shadow Justice minister, said he would want Britain to stay in the European Union "come what may".
However Mr Corbyn has failed to offer enough reassurance to Labour MPs that he would back continued membership of the 28-state bloc.
Last night at the weekly Parliamentary Labour party meeting Mr Corbyn told his fellow MPs that the party "can't just give Cameron a blank cheque" to back his renegotiation plan.
But Hilary Benn, the shadow foreign secretary, confused things when he said Mr Corbyn had told him that Labour "will stay to fight for a better EU".
He released a statement - signed off by Mr Corbyn - reinforcing his pro-European stance this afternoon, saying the party's position was to oppose possible Tory plans to opt-out from the EU's social chapter and vowing to opt back in if Labour wins power in 2020.
Speaking to the World at One, Lord Falconer said: "My view is that we should stay in the EU come what may, so whatever the result of the negotiations, I believe that Britain would be so damaged by leaving the European Union or indeed saying we would leave the European Union, that we should stay.
"If the Labour party adopts a position which says we might leave the EU and might argue against it, then of course my position would become impossible."
Mr Benn's statement read: “Being in Europe has protected and improved workers' rights in Britain, giving everyone statutory paid holiday, limits on working hours and improved maternity and paternity leave," Mr Benn said.
"We are strongly opposed to any attempt by David Cameron to try and weaken these, but the truth is if we want to protect workers' rights the answer isn't to leave the EU, but to get rid of this Tory Government.
“That's why the Labour Party has always been committed to not walking away, but staying in to work together for a better Europe.”
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