A committee of lawmakers said in a report published on Saturday, the British government must publish a detailed plan for Brexit by mid-February.
The government must set out its position on future membership of the European Union's single market and customs union.
Parliament's Exiting the EU committee also said the government should seek a transitional deal with the bloc.
It is made up of lawmakers from several parties including Prime Minister Theresa May's Conservatives and opposition Labour.
May has said she will begin formal divorce talks with the EU by the end of March.
She has come under fire from businesses, investors and lawmakers for having revealed little about the government's Brexit plans.
Six months have passed since the country voted to leave in last June's referendum..