Tory MPs have been warned Brexit could be delayed if they fail to fall in line behind Theresa May and support her deal.
Justice secretary David Gauke said the UK had to leave the EU in a “a smooth and orderly way”.
“The determination that the prime minister has set out is to deliver that on the 29th March but if we are going to do that then MPs do need to be backing a deal in short order, and that’s MPs both on my own side and also in other parties,” he told BBC Radio 4′s Today programme on Monday morning.
It came as May invited rebel Tory MPs into the heart of government on Monday to thrash out changes to her Brexit deal she hopes can overcome massive opposition in Brussels and Westminster.
Hardline eurosceptics in the European Research Group and Remain-supporting former ministers will form the Alternative Arrangements Working Group (AAWG), which Downing Street said would meet “regularly” with Brexit Secretary Stephen Barclay and senior officials.
ERG deputy chairman Steve Baker, former Northern Ireland secretary Owen Paterson and Yeovil MP Marcus Fysh will join forces with former education secretary Nicky Morgan and ex-Cabinet Office minister Damian Green to examine the feasibility of the so-called Malthouse Compromise.
The AAWG is due to meet at the Cabinet Office in Whitehall on Monday, with meetings also scheduled for Tuesday and Wednesday this week.
Baker, a former Brexit minister who quit last year in protest at the Chequers agreement, and Morgan were involved talks last week between MPs from the Remain and Brexiteer wings of the Conservative Party over the Malthouse compromise.
Drawn up in meetings co-ordinated by housing minister Kit Malthouse, it recasts the backstop as a “free trade agreement-lite”, with a commitment on all sides there should be no hard border and an extended transition period to December 2021.
It is seen as one of the main reasons the ERG changed its mind and backed an amendment last Tuesday tabled by Sir Graham Brady.
It requires the PM to replace the agreement’s controversial backstop with “alternative arrangements” to keep the Irish border open after Brexit.
May told the Commons last week it was “a serious proposal that we are engaging with sincerely and positively”.
The new grouping was announced as former foreign secretary Boris Johnson accused the party leadership of using rumours of a June general election, which appeared in Sunday newspapers, as a “scare tactic” to bounce exhausted Conservative MPs into backing her Withdrawal Agreement.
He used his regular Monday Telegraph column to suggest that if someone in Tory HQ thought a summer election was a good idea they should be “dispatched on secondment to Venezuela or Zimbabwe or somewhere they can do less damage.”
Earlier, car giant Nissan hit out at Brexit “uncertainty” as it confirmed it would build its X-Trail 4×4 in Japan instead of at its Sunderland plant.