Brexit Secretary David Davis has ruled out demands for Parliament to be given a vote on triggering the formal negotiations to take out of the European Union.
The House of Lords Constitutional Committee has warned it would be “constitutionally inappropriate” for Theresa May to invoke Article 50 of the EU treaties without first obtaining the approval of both Houses of Parliament.
In a report on Article 50, the committee said MPs and peers must “play a central role” in the decision to launch negotiations, either by passing an Act of Parliament or approving resolutions tabled in both Commons and Lords.
It said MPs and peers should also have a key role in scrutinising the Brexit negotiations - due to take two years - and approving the final deal reached between the UK and the remaining 27 EU states.
But appearing before the Commons Foreign Affairs Committee, Mr Davis said the outcome of the EU referendum had been clear and that a vote against invoking Article 50 would set Parliament against the people.
“The Government position is that it is an exercise of Crown Prerogative. The theory of it is the Crown represents the nation,” he said.
“This is the only time that I am aware of in British history that the Crown Prerogative has been backed up by a 17.5 million vote mandate.
“A proposal that could put Parliament in opposition to the people over something as simple as this is an extraordinary one.”
Mr Davis also issued a sharp warning to peers not to try to block the legislative changes that will be needed for Britain to leave the EU.
“It is a very, very, very clear mandate and I think the House of Lords would be quite unwise not to take that mandate seriously,” he said.
“I would be very surprised if they were unwise enough to go down the route of just blocking it full stop.”
In its report, the committee warned that it was “unclear” whether the UK could unilaterally halt Article 50 talks once they have been triggered, if it changed its mind about wanting to leave.
It said Parliament should act on the assumption that Article 50 is “irreversible” and should allow it to be invoked only when it is in the UK’s best interests to begin negotiations.
Committee chairman Lord Lang of Monkton said: “The referendum result was clear and it is right that the Government are preparing to take Britain out of the EU.
“However, our constitution is built on the principle of parliamentary sovereignty and the decision to act following the referendum should be taken by Parliament.”