British Prime Minister Theresa May has offered to give lawmakers some scrutiny of the process to leave the European Union on condition they did not "undermine" her negotiations with 27 other members of the bloc.

May has said she will trigger the formal EU divorce by the end of March but that she will not provide a running commentary on the process. She also said it is for ministers to decide when and how to trigger the EU exit by invoking Article 50 of the Lisbon Treaty.

Lawmakers from the opposition Labour Party proposed a motion in Parliament that called for a full debate on the government's plan to leave the EU and demanding Parliament be "able properly to scrutinize that plan for leaving the EU before Article 50 is invoked."

In an amendment proposed under May's name and posted on the Parliament website, the government said: "The process should be undertaken in such a way that respects the decision of the people of the UK when they voted to leave the EU."

Any scrutiny must "not undermine the negotiating position of the Government as negotiations are entered into which will take place after Article 50 has been triggered," according to a copy of May's amendment.