Prime Minister Boris Johnson plans to pass a law guaranteeing Britain's Brexit transition period cannot run beyond the end of 2020, a source in his office said on Tuesday.
Johnson won a big majority in last week's election on a promise to take Britain out of the European Union by the end of January, followed by a transition period when London and Brussels negotiate a trade agreement.
European leaders have said the December 2020 deadline would be too tight to complete a comprehensive deal and the main opposition Labour party says Johnson's proposal could lead to a no-deal outcome.
"Last week the public voted for a government that would get Brexit done and move this country forward -- and that's exactly what we intend to do, starting this week," a Downing Street source said.
"Our manifesto made clear that we will not extend the implementation period and the new Withdrawal Agreement Bill will legally prohibit government agreeing to any extension."