Legislation was given royal approval this week that would mean it is illegal for Britain's prime minister Boris Johnson to take the UK out of the European Union without either an agreement or the consent of parliament on October 31st 2019.

Queen Elizabeth II provided royal assent hours before a five-week shutdown of parliament was initiated.

Last week, parliament passed what became known as 'no-deal legislation', which forces Mr Johnson to ask the EU for another three-month extension to the Brexit deadline unless a new withdrawal agreement can be approved or parliament votes to allow a no-deal divorce by October 19th.

Known as the Benn Bill, it means the Brexit deadline would be pushed back until January 31st 2020 should neither of these conditions take place.

This comes despite Mr Johnson's promise to take Britain out of the EU by Halloween, regardless of whether or not a deal was on the table.

However, any extension to Brexit now has to be agreed to by all other 27 member states of the EU - and it is possible that the other leaders will decide against yet another delay, given that two prior deadlines have already come and gone.

In addition, should the EU respond with a different date in mind, Mr Johnson would be forced to accept it unless there is an MP vote to reject it within two days.

It has been suggested that Mr Johnson could refuse to write or sign the letter to the president of the European Council necessary to request an extension, but this is likely to lead to court action against him.

Foreign secretary Dominic Raab has been quoted as saying the government intends to adhere to the law, but "test to the limit what it actually lawfully requires".

Meanwhile, HM Treasury told Reuters in response to a Freedom of Information request that it has received legal advice on the UK's rights and obligations on leaving the EU, but would not be publishing it.

"Release of this information at such a sensitive time would be detrimental to the government's negotiating position," a statement said.