Critics are trying to undermine Brexit negotiators, No.10 warns
Downing Street has accused opponents of Brexit of trying to tie the hands of UK negotiators in the upcoming talks on withdrawal from the European Union.
MPs and peers may get a chance to attempt to impose conditions on Britain's negotiating stance if the Supreme Court upholds a ruling that Theresa May must obtain parliamentary approval to start talks under Article 50 of the EU treaties.
Both Labour and Liberal Democrats have indicated they would seek to amend any motion coming before parliament as a result, with Jeremy Corbyn saying over the weekend that he would try to ensure that issues of market access and protections formed part of the UK position.
Other amendments could require the Government to publish a white paper on its negotiating goals or hold a second referendum on the outcome.
The Prime Minister's official spokeswoman said the Government wanted "everyone to be coming together" to focus on getting the best results for Britain from the process.
Anyone "backing the UK team" in the negotiations with the remaining 27 EU states should allow them the maximum possible flexibility, she suggested.
"While others are seeming to make clear that they want to frustrate the will of the British people by slowing down the process of leaving and trying to tie the Government's hands in negotiation, the Government is getting on with respecting what the British people decided and making a success of Brexit," the PM's spokeswoman told a regular Westminster media briefing.
"If you are backing the UK team, you want them to be able to go into the negotiation and get the best deal possible.
"It's very important that we are able to get the best deal possible, and that means not having our hands tied in negotiation."
The spokeswoman said that Mrs May was focused on respecting the decision to leave the EU made in the June 23 referendum and working out what Britain's new arrangements outside the bloc would look like.
"We are seeking to provide certainty where we can by saying we will trigger Article 50 by the end of March and that we are very clear there will be no going back," she said.
"That's why now we want everyone to be coming together to focus on how we get the best deal, supporting the approach the UK can take in what will be a difficult negotiation where there will be us and 27 others, and therefore enabling the Government to have the strongest position going into that negotiation, so we can get the right deal."
Shadow attorney general Baroness Chakrabarti insisted that if Parliament was given a say, MPs and peers would not veto Brexit.
She told the BBC Radio 4 Today programme: "We have been completely clear that we are democrats and respect the outcome of the referendum, even though many of us - myself included - campaigned in the opposite direction.
"So this will happen, pursuant to the will of the people. But there is not a simple question of 'in and out of the European Union', there are many questions that Parliament has to scrutinise about what happens next."
Mrs May will be given an indication of the scale of parliamentary opposition she faces over Brexit on Wednesday, with a potential revolt over demands for the Government to set out its plan for leaving the EU before triggering Article 50.
Labour will use an opposition day debate to force a Commons showdown on the issue, with dozens of Tories thought to be considering supporting the demand.
Conservative former minister Anna Soubry said she had read Labour's motion and "I have to say I can't see anything in it I don't approve of and could not support".
Threatening to rebel unless the Government tabled an acceptable amendment to the Labour motion, she told BBC Radio 4's World At One: "These things are incredibly important. This actually transcends party politics and tribalism."
As many as 40 Tories could revolt and back the Labour motion, the BBC reported, and Ms Soubry said: "Who knows what support is out there in the parliamentary party."
Former Tory leader Lord Howard told the programme: "I don't think it's reasonable to expect the Government to disclose its negotiating position.
"You can try and make distinctions between principles and details, but I don't think those distinctions stand up. If you are entering into a negotiation, the last thing you want to do is to disclose your hand before you start negotiating."
Liberal Democrat leader Tim Farron dismissed as "silly" the suggestion that his party is undermining UK negotiators' hand in the upcoming talks.
"The idea that the British people and their representatives have no role in this and it's just down to ministers and bureaucrats to decide our future - that would be a terrible stitch-up," Mr Farron told the Press Association.
"We are here to make sure that the public are heard and that the will of the people is actually done and at the end of the day, the people get their say over what kind of Brexit we have or whether indeed we decide we're going to stick with what we've got."
Mrs May spoke by phone with two new EU leaders - Croatia's prime minister Andrej Plenkovic, whose party won elections in September, and Estonian PM Juri Ratas, who took the top job in November after a cabinet split. They are due to meet at the European Council summit on December 15.
The Labour motion to be debated by MPs on Wednesday calls on Mrs May to publish her Brexit plan before triggering Article 50, but acknowledges "there should be no disclosure of material that could be reasonably judged to damage the UK in any negotiations".
Shadow Brexit secretary Sir Keir Starmer said: "Labour accept and respect the referendum and we will not frustrate the process of leaving the EU. But Parliament and the public need to know the basic terms the Government is seeking to achieve from Brexit. This issue is too important to be left mired in uncertainty any longer.
"That is why Labour have called this debate on Wednesday. Our motion is simple but would deliver real accountability and grip in the Brexit process. I hope MPs on all sides of the House will join Labour in supporting it."