The Brexit process has hit yet another snag today, as prominent Tory MPs who backed remaining in the EU during last year’s referendum are joining forces with a handful of Labour MPs to propose amendments to two important pieces of Brexit legislation. If agreed by MPs, these amendments would keep the UK in the customs union after the UK has withdrawn itself from the bloc. 

Anna Soubry and Ken Clark, who made the amendments, have the backing of some Labour MPs who backed Remain during the Brexit vote, which has increased speculation that Jeremy Corbyn’s party is moving to a softer stance on Brexit. Remainers believe it has a “serious prospect” of success if at least a dozen MPs from the Tory party also rebel. 

If the amendments are agreed, this would be a huge blow to Brexiteers who believe the UK must quit the customs union, and avoid any similar arrangement, in order to pave way for new global trade deals after leaving the EU.

On her third and final trade trip to China, prime minister Theresa May did not rule out such an arrangement, which would actually limit Britain’s ability to make free trade deals with non-EU countries, however, she failed to confirm that she thought should happen. 

There have been calls for the prime minister to clarify the government’s position on remaining in the customs union, as chancellor Philip Hammond and business secretary, Greg Clark, favour staying in the customs union for goods, as do Ken Clark and Anna Soubry. 

However, international trade secretary, Doctor Liam Fox, was swift to quash the notion, saying the government was considering a deal under which trade in goods would be covered by a customs union arrangement, while the UK would retain an independent policy on services. 

Accompanying the prime minister to China, Fox said that being part of a customs union would prevent Britain from setting its own trade regulation. “It is very difficult to see how being in a customs union is compatible with having an independent trade policy, because we would therefore be dependent on what the EU negotiated in terms of its trading policies, and we’d be following behind that,” he said.

When asked by Bloomberg reporters whether he was completely against the notion of Britain being part of a customs union in the future, Fox said: “We have to be outside of that to take advantage of those growing markets. One of the reasons we are leaving the European Union is to take control and that’s not possible with a common external tariff.”

Theresa May’s response was wishy-washy when trying to explain the government’s intention. “What I want to do is ensure that we have got the best possible trade arrangements with China and with other countries around the world once we have left the European Union,” she told Sky News on Friday.

“I do want to do those free trade agreements. There is more trade that we can do even before we get to those free trade agreements,” she continued.

Later on, a spokesperson for Number 10 was questioned on what the prime minister’s thoughts were about being part of a customs union, however, their answer did not provide a modicum of clarity. He said that May had an “open mind” to the kind of customs arrangement the UK has with the EU after Brexit and the transitional period. 

The spokesperson also backed up Fox’s statements, saying that he had been speaking for the government and confirmed that the PM was sticking by her statement from her Lancaster House speech that the UK does not intend to be bound by the common external tariff after leaving the EU. This would rule out the UK being part of the customs union. 

The split within the Conservative Party also comes as Theresa May’s leadership is under increasing scrutiny, both from hardline Brexiteers who believe that she is moving towards a softer Brexit, and backbenchers who are concerned that leaving the EU is a major distraction for the prime minister from building a strong domestic agenda.