Britain's government on Thursday published a draft law that would authorize Prime Minister Theresa May to begin the procedure for leaving the European Union in an important milestone towards Brexit.

"The British people have made the decision to leave the EU... so today we have introduced a bill in parliament which will allow us to formally trigger Article 50 by the end of March," said Brexit minister David Davis.

The two clause "European Union Notification of Withdrawal Bill" asks parliament to give May authority to start the formal mechanism by which Britain will leave the bloc.

The government said MPs would get their first chance to debate and vote on it on Tuesday and Wednesday next week.

May's government was forced to go to parliament following a landmark Supreme Court ruling this week that rejected its argument that executive powers allowed it to proceed.

The ruling Conservatives have a small majority in the House of Commons and the bill is expected to get the go-ahead from MPs, although opposition parties have said they plan put forward amendments that could slow it down.

Davis said he hoped that parliament would "respect the decision taken by the British people and pass the legislation quickly," arguing that MPs had supported holding the referendum in the first place.

Britain voted to leave the European Union in a referendum on June 23 last year following a bitter campaign and divisions have persisted since then.

A majority of Britain's 11 Supreme Court judges on Tuesday ruled that withdrawing from the EU meant there would have to be changes in Britain's domestic laws and therefore parliament had to be involved.

The main opposition Labour Party has said it is planning amendments including a clause calling for the protection of workers' rights, while the Scottish National Party wants to put forward dozens of changes.