London (CNN) Theresa May suffered the worst day in parliament for a British government in 40 years, losing three crucial votes as lawmakers moved to seize control of the faltering Brexit process.

The Prime Minister's authority was left hanging by a thread after Members of Parliament found her government in contempt for failing to publish the full legal advice underpinning her Brexit plan.

In a further and potentially more important defeat, lawmakers approved an amendment that aims to give Parliament greater say if May's Brexit deal is rejected next week. Parliament could then insist on a "softer" Brexit -- where the UK would remain in or closely aligned with the EU's customs union and single market, or even demand a second Brexit referendum.

MPs had already rejected a government compromise on the legal advice, under which the issue would have been kicked to a parliamentary committee. No British government has suffered a worse day at the hands of MPs for 40 years.

May's minority administration -- notionally propped up by the Democratic Unionist Party of Northern Ireland -- was left in turmoil as it became clear it could not win support for crucial votes in the House of Commons.

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