British Prime Minister Theresa May has accused the Labour Party of dragging its feet over cross-party Brexit talks as discussions resumed following the Easter break.
Mrs May acknowledged that Jeremy Corbyn's party was approaching the talks in a "serious" way but said they had hit difficulties over timetabling, with Conservatives pressing for greater urgency.
With Conservative MPs openly calling for Mrs May to name a date for her departure as Prime Minister, Downing Street is attempting to secure agreement in time to avoid holding European Parliament elections next month.
Officers of the Tory backbench 1922 Committee were meeting in Westminster on Tuesday to consider proposals to change party rules to allow MPs to challenge Mrs May's position as leader as early as June.
Meanwhile, the Remain-backing Change UK unveiled Boris Johnson's sister Rachel and former BBC correspondent Gavin Esler as candidates for the 23 May European elections while Nigel Farage announced former communist Claire Fox would stand for the Brexit Party.
At the first meeting of Cabinet since the Easter recess, ministers discussed the progress of cross-party talks, including the impasse over Labour's insistence on future involvement in a customs union with the EU.
Mrs May's official spokesman told reporters: "The Prime Minister said discussions with Labour had been serious but had also been difficult in some areas, such as in relation to the timetable for the negotiations.
"The PM said the Government's position was that progress needed to be made urgently as it was vital to deliver on the result of the referendum and for the UK to leave the European Union as soon as possible."
Mr Corbyn, however, put the blame for lack of progress on the Government's refusal to shift on its "red lines".
"We'll continue putting our case but quite honestly there's got to be change in the Government's approach," said the Labour leader.
"They cannot keep on just regurgitating what has already been emphatically rejected three times by Parliament, there's got to be a change."
He added: "What we're saying is that there must be a dynamic relationship, protection of rights at work, rights on what we consume and protection of our natural world as well as, of course, access to markets... and a customs union which would ensure there is no hard border in Northern Ireland.
"People might have voted to leave or to remain in the referendum nearly three years ago - they didn't vote to lose their jobs, they didn't vote to have a de-regulated society."
Talks at the Cabinet Office involved Mrs May's effective deputy David Lidington, Brexit Secretary Stephen Barclay and chief whip Julian Smith on the Government side, and shadow Brexit secretary Sir Keir Starmer, shadow chancellor John McDonnell, along with shadow cabinet ministers Rebecca Long-Bailey and Sue Hayman for Labour.
It is thought the government could seek to accelerate progress by tabling the Withdrawal Agreement Bill (WAB) in the Commons as early as next week, even if cross-party talks have not reached a conclusion.
Ministers are wary of putting the bill before MPs unless they are confident of getting it safely through the Commons. The bill which ratifies the UK's Brexit agreement and its passage is essential for EU withdrawal.
If it is defeated, it cannot be re-tabled unless the government brings the parliamentary session to an end and presents a new legislative programme in a Queen's Speech, introducing delays which would almost certainly dash hopes of avoiding the European elections.