Theresa May must reveal the government's plan for Brexit by mid-February, a cross-party committee of MPs has said.
In its first report, the Exiting the EU committee, chaired by Hilary Benn, demands ministers must set out their position on the UK remaining a member of the European single market and customs union.
May is due to deliver a long-awaited speech "setting out more" of her Brexit plan on Tuesday, which could come on the same day the Supreme Court rules on the government's appeal as to whether it has the right to trigger Article 50 without consulting MPs first.
The prime minister has so far revealed very little of the government's plan for negotiations with the other 27 EU member states once Article 50 is triggered, although she has repeatedly hinted that ending freedom of movement will be prioritised over single market membership.
Former shadow foreign secretary Benn said the committee, unique in counting MPs from all four nations of the UK among its members, was "not asking the government to give away its red lines or negotiating fall back positions".
"But we do want clarity on its broad aims given the significance and complexity of the negotiating task. This White Paper must be published by mid-February to give Parliament and the devolved governments time to scrutinise it," he added.
May had previously said she intended to trigger Article 50 by the end of March, starting a two-year negotiating process that will end with the UK leaving the EU.
In its report, the Exiting the EU Committee calls for transitional agreements to be included in negotiations across a host of areas to mitigate the risk of not being able to reach final agreements within the two-year window.
Pan-European cooperation on defence, foreign policy, security, financial crime, and counter-terrorism should "not be brought to an abrupt end" by Brexit, the report says.
“Ministers should aim to conclude negotiations on trade and market access with the EU-27 by the end of the Article 50 process. However, if a final ratified agreement is not reached by the time the UK leaves the EU, it would be in the interests of both sides to agree a provisional outline framework on the UK’s future trading relationship with the EU," Benn said.
“Whatever deal is concluded, Parliament must be given a vote on it and the government should make this clear now.”
Responding to the committee's report, a Department for Exiting Europe spokesperson said the government was "committed to creating a global Britain and we will continue to be a bold, outward looking nation."
The spokesperson added: “We want a smooth and orderly exit from the EU, and will look at the best way to deliver that.
"We've also said we will set out our plans, subject to not undermining the UK negotiating position, by the end of March and that Parliament will be appropriately engaged throughout the process of exit, abiding by all constitutional and legal obligations that apply."
Matthew Champion is a deputy world news editor for BuzzFeed News and is based in London.
Contact Matthew Champion at firstname.lastname@example.org.
Got a confidential tip? Submit it here.