An opposition Labour lawmaker requested on Wednesday an emergency debate in parliament on Brexit, seeking to challenge Prime Minister Theresa May's pursuit of a short delay to Britain's departure from the European Union, her office said.

May is expected to ask the EU for a short delay to Brexit later on Wednesday, a move which has prompted some lawmakers to say she is forcing them to choose between her deal and leaving the EU without an agreement.

The office of Alison McGovern, the Labour lawmaker, said the so-called SO24 emergency debate motion would be a very short statement on Brexit and would be aimed at securing a debate in parliament. It is not clear if that would trigger a vote.

It is up to parliament's speaker to decide whether to press ahead with the move, after which McGovern would make a three-minute speech on the case for such a debate and then parliament would have to agree that the debate should take place.

The speaker, who blindsided the government earlier this week by saying May could not ask parliament to vote on her deal for a third time unless it was substantially different, could allow lawmakers to propose changes to what will be a neutral statement.

That might open the way for parliament to debate and vote on different options for the way forward on Brexit. So far, it is not clear whether this will happen.