Conservative Chancellor Philip Hammond has been "hijacked" by his pro-Brexit cabinet colleagues, according to Labour's Chuka Umunna.
The Vote Leave Watch founder made the claim after Hammond, previously seen as one of the most pro-EU voices in Theresa May's top team, published an article with Eurosceptic International Trade Secretary Liam Fox in the Sunday Telegraph.
The top Tory duo confirmed that the UK government would split from the EU's single-market and customs union in 2019, while seeking a transitional deal from Brussels so that British businesses do not face a so called "cliff edge".
"We will leave the single market, because there was a vote for change on June 23rd and that is what we will deliver," Hammond and Fox wrote.
"We want our economy to remain strong and vibrant through this period of change. That means businesses need to have confidence that there will not be a cliff edge when we leave the EU in just over twenty months' time."
The show of unity, after a summer of in-fighting over Brexit in the cabinet, prompted Umunna – who wants the UK to remain in the EU's single market and customs union – to speak out.
"The Chancellor – talked of as the voice of reason in Cabinet – has been taken hostage by those arguing for a job-destroying Brexit," he told his Twitter followers. "There is a consensus that it will be impossible to finalise all the arrangements for our withdrawal from the EU by March 2019. A meaningful transition is essential and it makes sense for us to be in the single market and customs union during that period."
Labour's position on staying or splitting from the EU's single-market and customs union is unclear, with Jeremy Corbyn's shadow cabinet issuing contradictory statements on the issue. The party's general election manifesto promised to scrap the Tories' Brexit White Paper and place "a strong emphasis" on retaining the benefits of the single-market and customs union.
But staying in the single-market would mean that the free movement of EU nationals to the UK would continue and maintaining Britain's position in the customs union would mean that the government would not be able to broker free trade deals with non-EU nations.
"Freedom of movement will end when we leave the European Union. Britain's immigration system will change, but Labour will not scapegoat migrants nor blame them for economic failures," the manifesto also reads.