The UK government became the first in the nation's history to lose a contempt of Parliament vote over its handling of legal advice about its proposed Brexit deal.

British Prime Minister Theresa May suffered an extraordinary three parliamentary defeats in a single day, as rebellious MPs at Westminster sought to wrest back control of Brexit.

The vote on Tuesday found the government in contempt of Parliament for ignoring a Commons vote demanding publication of its legal advice. In response, the government was due to publish it on Wednesday, after ministers agreed to release the advice in full.

MPs had already voted down a government compromise, which would have referred the dispute to Parliament's privileges committee, delaying it until after next week's crunch vote on May's deal.

MPs then inflicted a third defeat, passing a cross-party amendment aimed at strengthening the hand of Parliament if the deal is voted down.

Security and immigration will be the focus of the second of five days of debate in the Commons, where Tuesday's marathon session extended into the early hours.

UK ministers forged ahead with efforts to win over MPs on Wednesday, with another eight hours of debate due.

May was set to face Labour leader Jeremy Corbyn at prime minister's questions at midday, before the Brexit debate got under way.

On Monday, the government's chief legal adviser, Attorney General Geoffrey Cox, had published a summary of his legal advice, but that did not satisfy MPs who said the advice should have been published in full.

Cox told MPs on Monday that his advice contained no bombshells and should remain private.

Labour called for the immediate publication of the advice along with the Liberal Democrats, the Scottish National Party, the Democratic Unionist Party, Plaid Cymru and the Green Party.

MPs can now use the government's legal advice in their decision-making process ahead of Parliament's Dec 11 vote on May's deal, which sets out how the UK will interact with the European Union after it withdraws from the bloc at the end of March.

May's deal is unpopular among MPs and is likely to be defeated, according to current projections.

The uncertainty could trigger May being unseated as prime minister, the calling of a general election, and possibly a reopening of negotiations with the EU, as well as potentially unleash a so-called people's vote during which the UK's electorate would again be asked whether the UK should leave the EU.