The shadow secretary of state for Northern Ireland has reacted sceptically to the idea of calling a referendum on Irish unity after Brexit.
"I don't think it's remotely clear at the minute that those conditions arise," said Tony Lloyd.
He told the NI Affairs Committee it was "probably not the most obvious thing that we ought to rush into".
Sinn Féin president Mary Lou McDonald has called for a border poll in the event of a no-deal Brexit.
Mrs McDonald was speaking after meeting Theresa May on the final day of her two day visit to Northern Ireland.
She said that a taking Northern Ireland out of Europe via Brexit, despite a majority of people in Northern Ireland voting to Remain, meant that the "concept of consent had been damaged".
Under the terms of the Good Friday Agreement, the Secretary of State has to call a border poll if it appears likely there would be a majority for a united Ireland.
NI Secretary Karen Bradley, whose responsibility it is to call a border poll, said on Wednesday that it was not "in any way sustainable" to believe that most people in Northern Ireland supported a united Ireland because a majority voted for Remain in the Brexit referendum.
At the NI Affairs Committee, Mr Lloyd acknowledged there have been calls for a referendum.
"There certainly are voices that argue circumstances have changed but probably this isn't the most propitious time to begin that conversation," he said.
Mr Lloyd told the committee he "very much doubts" that the UK will leave the the EU on 29 March.
He said he finds it difficult to believe the prime minister will be able to achieve the deal she wants by that deadline.
"We need to have some sense of realism," he added.
Mr Lloyd said it was not Labour policy to extend the Article 50 deadline.
Speaking in Belfast, Mrs McDonald that "polling data north and south" showed that the public favoured a United Ireland in the event of a "crash Brexit".
She added: "So if there is a Tory crash, and Mrs May has conceded as much on the floor of the House of Commons, in that event, not alone will there be pressure for a referendum on Irish unity, there will be absolute democratic imperative to call such a referendum."
The prime minister's official spokesman told reporters in Westminster: "The conditions for a border poll are set out in the Belfast Agreement.
"It remains the Northern Ireland Secretary's view that the majority of the people of Northern Ireland continue to support the current political settlement and that the circumstances requiring a border poll are not satisfied."