THERE will be no UK Government U-turn on Britain leaving the European customs union, No 10 has made clear, as it insisted ministers were pursuing a smooth Brexit “as one”.

Amid suggestions that the so-called “three Brexiteers” of Boris Johnson, Liam Fox and David Davis were preparing to use a meeting this Wednesday of a Brexit sub-committee to reject Theresa May’s preferred option for future custom arrangements with the EU, Downing Street stressed how Britain would leave the current customs union and would not, as Labour has proposed, join a new one.

“I note we are back into the season of lots of Brexit speculation,” declared the Prime Minister’s spokesman as he rebuffed talk that Mrs May would regard as a motion of no confidence in her Government the successful passing next month of an amendment to the Trade Bill, backed by Tory rebels, calling for Britain to stay in the customs union.

He noted how the BBC story on the subject was an “absolute mystery” and had subsequently disappeared from its bulletins.

On a campaign visit to a business in the West Midlands, the Conservative leader insisted leaving the customs union would allow the UK to strike new trade deals around the world, stressing that she was seeking a "frictionless" border with the EU.

Early indications suggested that the PM had allayed fears among the Brexiteers that she was wobbling on the customs issue.

The Government has put forward two options for future customs arrangements with the EU once Britain ends its implementation period in December 2020.

These are: a customs partnership, which would mirror completely the EU's rule - regarded by No 10 as “intellectually perfect” - and which would do away with any border checks and a "highly stream-lined arrangement", using technology to minimise disruption but which would involve minimal checks.

Asked which one the PM preferred, her spokesman replied: “We have put forward two options. They were set out in the Mansion House speech and elsewhere. Those are still the two options we are moving forward with.”

He went on: “We are absolutely clear that we are leaving the customs union and we will be free to strike out own trade deals around the world.”

Asked if there was any expert view that the UK Government’s options, which have been public for months, would work, he replied: “Both of the two options we have put forward can provide solutions to the Irish border[issue] and to having a smooth customs arrangement with the EU.”

Asked if the two options had full support of Mrs May’s senior colleagues, he added: “Both options were set out in the Mansion House speech and in the paper published last summer and the Government has been moving forward as one with the process of leaving the EU.”

Senior pro-EU backbenchers on Thursday will stage a debate, calling on the UK to stay in the or a customs union with the EU. Given the dozen or so Tory rebels, it is likely the Government will be defeated in the vote following the debate. However, it is non-binding.

No 10 suggested the Government was not taking the vote too seriously as it pointed out, when asked if ministers would attend, that it was a “routine backbench business debate”.

John Whittingdale, the Brexit-supporting former Culture Secretary, told BBC News Thursday’s symbolic vote would be "a piece of theatre" but would have "no significance at all".

Earlier his Tory colleague John Redwood branded the European customs union a "protection racket," which hit trade with countries outside the EU.

It resulted in "very bad terms of trade, particularly on food, with poorer countries", he told BBC Radio 4's Today programe, adding: "It means we can't buy cheaper South African oranges, we have to buy dearer Spanish ones."

The pro-Brexit former Welsh Secretary asked if Mrs May could remain in office if she performed a U-turn on leaving the customs union, Mr Redwood said: "I don't think that's in question because I hear she is not changing her mind and that is extremely good news."

Meanwhile, Ken Clarke, the pro-EU former Chancellor, claimed the customs issue had become the "panic of the day" in Downing Street.

"The key vote is on the Trade Bill in about a month's time with the amendment that Anna Soubry and I have put down," he told Today.

Mr Clarke added: "Parliament has got to decide: what is the national interest, this is a big subject."

The veteran Europhile said an "absolute red line is we should not break the Good Friday Agreement" and should not be dismissed as an "inconvenience".

He added: "It's the next big problem and it will need all this to be resolved over the next month or two because...we won't make much progress until the Irish problem is solved.”