A cross-party group to co-ordinate the parliamentary fight against a "hard Brexit" has been set up under the leadership of Tory former minister Anna Soubry and senior Labour MP Chuka Umunna.
The all-party parliamentary group (APPG) on EU relations could cause difficulties for Theresa May as she attempts to steer Brexit legislation through the Commons, relying on the support of the Democratic Unionist Party.
As well as working together in Parliament, the APPG will collect evidence from business groups, trade unions and charities about their views on Brexit.
The MPs in the group believe Parliament cannot be "spectators" accepting information from ministers, but should instead be "active players" in the Brexit process, independently seeking out information to inform voting decisions on the deal eventually negotiated by the UK Government.
Streatham MP Mr Umunna, who led a Labour revolt over Brexit last month by calling for the UK to stay in the single market, and prominent Remain campaigner Ms Soubry are the group's co-chairmen.
Liberal Democrat deputy leader Jo Swinson, the SNP's international affairs spokesman Stephen Gethins, Green co-leader Caroline Lucas and Plaid Cymru's Jonathan Edwards are vice-chairmen.
The formation of the APPG follows weeks of private conversations between MPs of different parties and they will work closely with pro-European pressure groups Open Britain, Vote Leave Watch, Best for Britain, British Influence and the European Movement.
Mr Umunna said: "The General Election result was an instruction by the British people for parliamentarians to put their differences to one side and co-operate in the national interest.
"We won't accept MPs being treated as spectators in the Brexit process, when we should be on the pitch as active players representing our constituents.
"We will be fighting in Parliament for a future relationship with the EU that protects our prosperity and rights at work, and which delivers a better and safer world."
The announcement of the group comes amid concern from Brexit supporters that attempts will be made to "stymie" withdrawal from the EU.
Former Brexit minister David Jones used a Mail on Sunday column to claim that "fanatically pro-EU MPs, both Labour and misguided Tory ones, too, have hatched a cunning plot" to water down Brexit by keeping the UK in the single market and customs union.
He said: "Parliament exists to reflect and enact the will of the people - not to subvert it. But amid the heat of high summer, it looks very much as if a plot is under way at Westminster."