DOMINIC Raab has hinted the UK Government could mount a legal challenge to the law that orders Boris Johnson to seek a Brexit extension to January 31.

As the Prime Minister prepares to travel to Luxembourg for a working lunch of snails, salmon and cheese with Jean-Claude Juncker, the outgoing European Commission President, the Foreign Secretary responded to suggestions Mr Johnson might be prepared to ignore the extension bill as he repeatedly maintains he would under no circumstances seek to delay Brexit further beyond October 31.

READ MORE: Boris Johnson to tell Jean-Claude Juncker UK will reject any Brexit delay offer 

"The UK Government is always going to behave lawfully; the suggestion otherwise is nonsense,” declared Mr Raab, stressing: "We, of course, take these considerations very seriously.”

But he then added: “At the same time, the legislation that was required, the surrender bill, is deeply, deeply flawed."

At the weekend, it was suggested Downing St was preparing itself for a “major court battle” with Dominic Cummings, the PM’s de facto chief of staff, allegedly telling colleagues: “The constitutional crisis is only just beginning.”

Tomorrow, the UK Supreme Court begins its adjudication as to whether or not Mr Johnson's decision to prorogue Parliament for five weeks is lawful. A decision is due at the end of the week.

Mr Raab dismissed the notion – floated by Stephen Barclay, the Brexit Secretary - that the Brexit transition period, due to end in December 2020, could be extended by as much as two years.

"No, it is not something under consideration," he told BBC Radio 4’s Today programme.

The Foreign Secretary insisted the details of a deal were “being shared” with the EU27 but Tytti Tuppurainen, Finnish European affairs minister, said the UK still had not put forward any proposals that could "compensate" for the removal of the Irish backstop.

"We have to remain open and see what happens in the domestic politics of the United Kingdom," she said as she arrived at a meeting of EU ministers in Brussels.

"Of course, the European Union is always ready to negotiate when a proper proposal from the United Kingdom side is presented. So far I haven't seen any proposal that would compensate the current backstop in the Withdrawal Agreement," she added.

READ MORE: Mark Smith: A pro-independence majority at Holyrood is not a mandate for another referendum. It’s time we changed the rules 

Ahead of his first meeting with Mr Juncker, the PM insisted he believed "passionately" that a new Brexit deal could be struck with Brussels but he will warn the Commission President he will reject any offer to delay Britain's departure.

Writing in the Daily Telegraph, Mr Johnson said he was working "flat out" to reach an agreement but reiterated that he would take the UK out of the bloc even if a deal cannot be reached at the European Council summit next month.

"If we can make enough progress in the next few days, I intend to go to that crucial summit on October 17 and finalise an agreement that will protect the interests of business and citizens on both sides of the Channel, and on both sides of the border in Ireland.

"I believe passionately that we can do it, and I believe that such an agreement is in the interests not just of the UK but also of our European friends.

"We have all spent too long on this question. And if we can get that deal, then of course there will be time for Parliament to scrutinise and approve it before the end of October.

"But be in no doubt,” he declared, “that if we cannot get a deal - the right deal for both sides - then the UK will come out anyway."

The PM will also hold talks with Xavier Bettel, Luxembourg's premier, and Michel Barnier, the EU's chief negotiator.

A No 10 source said: "The Prime Minister could not be clearer that he will not countenance any more delays. We will be leaving on October 31 no ifs, no buts.

"Any further extension would be a huge mistake. It is not just a question of the extra dither and delay; it is also the additional long months of rancour and division, and all at huge expense. We must finally deliver on the 2016 referendum result.

"This is why the PM will stress to Mr Juncker that, while he wants to secure a deal, if no deal can be agreed by October 18 his policy is to leave without a deal on October 31 and reject any delay offered by the EU."

Downing St has sought to downplay speculation that today’s meeting could be a breakthrough moment and Mr Barclay said yesterday there was still "significant work" to do to reach an agreement.

However, he insisted a "landing zone" for a deal was in sight, telling Sky News's Sophy Ridge On Sunday that there had been "extensive talks" at a technical and a political level.

Over the weekend, Mr Johnson likened Britain leaving the EU to the Incredible Hulk, telling the Mail On Sunday: "Hulk always escaped, no matter how tightly bound in he seemed to be; and that is the case for this country."

But his comparison was described as "infantile" by Guy Verhofstadt, the European Parliament's Brexit co-ordinator, who questioned: "Is the EU supposed to be scared by this?"

And David Gauke, the former Justice Secretary, stressing how the PM must obey the law on Brexit, noted: “Maybe the Incredible Hulk doesn't have to comply with the law but the British Government does.

"And if Parliament has neither supported a deal, nor supported a no-deal departure, then the law is clear that he has to seek an extension, the Prime Minister has to seek an extension and that is what he will have to do. That is what the law states."