The British government must publish a detailed plan for Brexit by mid-February, setting out its position on future membership of the European Union's single market and customs union, a committee of lawmakers said in a report published on Saturday.
The Exiting the EU committee, made up of lawmakers from several parties including Prime Minister Theresa May's Conservatives and opposition Labour, also said the government should seek a transitional deal with the bloc.
May has said she will begin formal divorce talks with the EU by the end of March but has come under fire from businesses, investors and lawmakers for having revealed little about the government's Brexit plans.
"The government needs to publish its Brexit plan by mid-February at the latest, including its position on membership of the single market and the customs union, so that it can be scrutinised by parliament and the public," said opposition Labour lawmaker Hilary Benn, chair of the committee.
May has said giving a running commentary on preparations would weaken her hand in negotiations. She is due to say more about her approach to Brexit in a speech on Tuesday.
The committee said the Brexit plan must be presented in the form of a government policy document, alongside economic assessments of various options for market access and trade.
"We're not asking the government to give away its red lines or negotiating fall-back positions, but we do want clarity on its broad aims," said Benn.
The committee called on the government to seek to ensure continued access to EU markets for financial services firms and avoid the imposition of tariffs.
It also said May should commit to giving parliament a vote on the final Brexit deal.
The Telegraph newspaper reported that Labour planned to use the government's expected defeat this month in a court battle on how Brexit talks can be triggered to push for parliament to be given a veto on the final package.
The Supreme Court is due to rule on whether the government can use executive powers to kickstart the talks, as it had planned to, or whether it needs parliament's assent.
The Telegraph said that if the ruling required parliament to vote on a bill to trigger Brexit, Labour would put forward an amendment demanding lawmakers get a vote on the final deal as well.
Labour alone could not win a vote on such an amendment. The Telegraph said the party was sounding out Conservative lawmakers who were against Brexit to see if they would support such a move.