Jeremy Corbyn refuses to say if he will force his MPs to back Brexit
Labour faced accusations that it was being "cannibalised" by Ukip and the Liberal Democrats, as Jeremy Corbyn again refused to say whether he will force his MPs to back Brexit.
Amid threats of a rebellion, Mr Corbyn said he would "ask" Labour MPs to respect the result of the EU referendum and back the triggering of Article 50 to begin the formal Brexit process.
Prime Minister Theresa May could be forced to seek parliamentary approval for the formal step needed to start Brexit negotiations if the Government loses its Supreme Court appeal next week.
The Labour leader is facing a revolt, with suggestions that dozens of MPs in Remain-voting seats as well as peers could vote against triggering Article 50.
Former deputy prime minister Nick Clegg criticised the "absolute lack of clarity" from Labour.
But asked if he would impose a full three-line whip on his MPs, compelling them to back it, Mr Corbyn told Sky News' Sophy Ridge on Sunday: "I will ask all Labour MPs to respect the result of the referendum and allow Article 50 to be opened so we start that two-year, probably longer, period of negotiation."
Mr Corbyn highlighted the difficulties Labour has with MPs representing both metropolitan Remain-voting constituencies and working class Brexit-backing areas.
He said the party will put down amendments to any legislation to pave the way for invoking Article 50 in an effort to get guarantees on issues like workers' rights, environmental protection and access to the single market.
Shadow Brexit secretary Sir Keir Starmer backed Mr Corbyn's assessment of the situation.
Asked on ITV's Peston on Sunday whether the leader would impose a three-line whip, he said: "That's not yet been determined.
"We're talking to colleagues, we don't know the outcome of the case.
"But I'm not going to pretend that this isn't difficult for the Labour Party. There are colleagues in the PLP (parliamentary Labour Party) who are very concerned, as I am, about the outcome of the referendum."
Sir Keir said Labour also wants a vote on the final deal of Britain's future relationship with the European Union.
He added: "I do not accept the proposition that on the second vote, which is the one that really counts, the new relationship, that we should have a vote that is a rock and a hard place.
"I don't accept that, and we'll be fighting that."
Mr Clegg said he would also bring forward amendments, including one to secure a referendum on the final deal.
But he warned Labour could be finished as an electoral force by the Brexit issue.
"I think there's a very real prospect now of the fate that occurred to the Labour Party north of the border, in one shape or form, will now happen south of the border," the former Lib Dem leader told BBC One's Andrew Marr Show.
"I think the Labour Party is in danger of being cannibalised by Ukip at one end and the Liberal Democrats at the other.
"I think this ambivalence and this absolute lack of clarity from Labour about the biggest issue of our time, sort of dithering rather helplessly in the middle of the road, is only going to make their fate even worse."
Tory MP Maria Caulfield said: " Labour are hopelessly divided and confused over how to respond to the referendum result.
"They can't agree over whether we should leave the single market, can't say whether they will have an agreed position in Parliament - and have said this morning they will also find new ways of frustrating the process of leaving.
"The Prime Minister has set out a plan to build a global Britain after exit and has been clear that Parliament will be properly engaged in the process and will vote on the final deal.
"Labour are flailing about, irrelevant, incompetent and completely out of touch with ordinary working people."