Britain will be poorer if MPs back Theresa May’s Brexit deal, Philip Hammond has admitted, as he prepared to publish new official forecasts.

In an extraordinary interview, the chancellor acknowledged that “remaining in the single market” – rejected by the prime minister – was the best way to secure the country’s economic future.

Asked if the fresh analysis would show that leaving the EU would be “detrimental”, he replied: “Yes, you are right in that analysis.”

Mr Hammond said: “Purely from an economic point of view, there will be a cost to leaving the European Union, because there will be impediments to our trade.”

And, asked if the forecasts would show it was “better to stay” in the EU, he added: “If you look purely at the economy, remaining in the single market would give us an economic advantage, yes.”

The comments come after Ms May tried to argue the UK could still be better off outside the EU under her withdrawal plans – ahead of a landmark vote by MPs on 11 December

Chancellor Philip Hammond: Brexit deal has many critics but its the best plan available to protect the economy jobs and businesses

Mr Hammond also appeared to acknowledge that parliament would dictate what happened next, if – as seems certain – the deal is rejected.

“We will have to look at the parliamentary arithmetic, look at the decision parliament has made and decide what is the best way to proceed,” he told BBC Radio 4’s Today programme.

A historic moment: thousands march to demand Final Say on Brexit Show all 65 1 /65 A historic moment: thousands march to demand Final Say on Brexit A historic moment: thousands march to demand Final Say on Brexit An estimated 700,000 people marched through London to demand a final say on the withdrawal agreement Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Red smoke from a canister hangs in the air as around 100,000 demonstrators march through London during a People's Vote anti-brexit demonstration savings banners and placards Anti-Brexit People's Vote March for the Future in London Rex A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Mayor of London Sadiq Khan takes part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum. PA A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018 Protesters wearing final Say shirts and holding placards Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit MP Chuka Umunna (left) and MP Vince Cable (right) as MP Anna Soubry (centre) addresses Anti-Brexit campaigners at a rally after the People's Vote March for the Future in London, a march and rally in support of a second EU referendum. PA A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit A People’s Vote march attendee calls for a Final Say Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Demonstrators with banners 'We're with EU' during the People's Vote March for the Future in London, Britain, 20 October 2018. Reports state that the 'March for the Future' is to be led by a column of young people and call for a Peopleâ€™s Vote on the Brexit deal. After marching through central London, there will be a rally on stage in Parliament Square, including speeches from Mayor of London Sadiq Khan. EPA A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Protesters at London’s march for the future in October The Independent A historic moment: thousands march to demand Final Say on Brexit Editor of The Independent Christian Broughton speaks to demonstrators in Parliament Sqaure after they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit A poster at the March for the Future in October The Independent A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum. PA A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018 Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum. PA A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Demonstrators hold placards as they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final say Brexit march - final say on our furture London, 20 October 2018 Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018 campaigner wrapped in EU flag Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say march for the future London, 20 October 2018 Credit: Angela Christofilou/The Independent Angela Christofilou/The Independent Angela Christofilou/The Independent A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018 Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Demonstrators pass Trafalgar Square as they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit Demonstrators wave Union and European flags and hold up placards as they pass Trafalgar Square, taking part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit Demonstrators hold placards as they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit A demonstrator holds a message during a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum. PA A historic moment: thousands march to demand Final Say on Brexit Demonstrators take part in the 'People's Vote March for the Future,' in central London, Britain, 20 October 2018. Reports state that the 'March for the Future' is to be led by a column of young people and call for a Peopleâ€™s Vote on the Brexit deal. After marching through central London, there will be a rally on stage in Parliament Square, including speeches from Mayor of London Sadiq Khan EPA A historic moment: thousands march to demand Final Say on Brexit A protester brandishes an Independent t-shirt during the Brexit March Angela Christofilou A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum PA A historic moment: thousands march to demand Final Say on Brexit Tens of thousands of people take part in People's Vote March for the Future in central London. The march organised by the People's Vote campaign is led by young people calling for a People's Vote on the Brexit deal Rex A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum PA

The prime minister used to insist that rejection of her deal would mean the UK crashing out of the EU with no agreement, but has recently admitted there could be “no Brexit at all”.

The government analysis is expected to say that GDP will be 1-2 per cent lower after 15 years of the prime minister’s proposals, compared with Britain staying inside the EU.

A ‘Norway-style’ relationship, remaining in the single market, would deliver a similar economic hit, while a ‘Canada-style’ free trade deal would swipe about 5 per cent from GDP.

The statistics could allow Ms May to argue that her deal offers very similar economic benefits to a Norway-style deal, while ending free movement of EU citizens.

They are also expected to show that a no-deal Brexit would leave GDP 7.6 per cent lower – equivalent to £150bn over 15 years.

In the interview, Mr Hammond argued Ms May’s deal offered “other benefits”, including control of borders, the ability to sign independent trade deals and fishing rights.

And, arguing Ms May’s deal would “minimise the economic impact” and be “entirely manageable”, he said: “The economy will be slightly smaller in the prime minister’s preferred version of the future partnership.

“The economy will continue to grow throughout that period because of fundamental strengths – this is a very modest impact.”

Refusing to concede that the deal was doomed to defeat, Mr Hammond added: “Nobody has yet come up with a better plan – this is by far the best way.”

The chancellor also said Downing Street was right to ignore a Commons motion to publish the full legal advice on the Brexit deal, saying it would be "impossible for the Government to function" if such confidential material was made public.