Labour has threatened to wage "hand-to-hand combat" with the Government on Brexit after the Supreme Court ordered that Parliament must have the final say on triggering withdrawal from the European Union.
Shadow foreign secretary Emily Thornberry said Labour would insist on a white paper on leaving the EU as the Government hurries to rush emergency Brexit legislation through Parliament in the coming days.
MPs and peers will have the last word on withdrawal after Prime Minister Theresa May lost the Government's appeal against a High Court judgment stating Parliament, not Downing Street, must invoke the Article 50 of the Lisbon Treaty mechanism that formally launches Brexit.
Ms Thornberry made it clear Labour would not let the Government get its own way.
"Article 50, if it it is going to be triggered, we will not get in the way of it, but we will try and amend the legislation in order to ensure that they keep coming back, that we keep an eye on them," she said.
"And, if necessary, there will be hand-to-hand combat on this," she told BBC's Newsnight.
Ms Thornberry said the Prime Minister must accept the role of Parliament in the process.
"She can"t say that she acts on behalf of the whole country without actually negotiating with Parliament, without listening to Parliament," she said.
"The plan, it may be a piece of paper with 'plan' written on the top, but it is a speech which she didn't make in Parliament, and she wasn't answerable to questions, and so we want to have a white paper."
Labour MP Stephen Kinnock told the BBC: "The Government has a mandate to take the UK out of the the European Union, they do not, in my view, have a mandate to turn us into some sort of European version of the Cayman Islands."
Legislation is likely to be introduced "within days" to keep Mrs May's timetable for leaving the EU on track, after the Prime Minister suffered defeat in a historic legal battle over Brexit.
By a majority of eight to three, judges at the Supreme Court rejected the Government's plan to use prerogative powers to trigger withdrawal talks under Article 50 of the EU treaties, ruling that ministers must first obtain the consent of Parliament.
Downing Street insisted the ruling would not derail the Prime Minister's deadline of invoking Article 50 by the end of March and Brexit Secretary David Davis told the House of Commons that a "straightforward" bill would be tabled to give effect to the decision of British voters.