Theresa May is facing questions from Eurosceptic MPs, who have banded together to launch a new campaign to push for a “hard Brexit”, the second group to have formed in just over a week.
The group, Leave Means Leave, aims to end the UK's membership of the European Single Market, simultaneously scrapping free movement.
The group is backed by MPs including former justice minister Dominic Raab, former environment secretary Owen Paterson and former defence minister Sir Gerald Howarth.
It will be led by Leave.EU co-founder Richard Tice, who also ran commercial property business CLS Holdings.
Other supporters including Labour donor and JML founder John Mills.
The group is another demonstration of the top level divides within the Conservatives in the aftermath of the June referendum.
It comes after foreign secretary Boris Johnson lent his support to a Brexit pressure group led by Labour MP Gisela Stuart.
And seperately, Downing Street last week refused to back Brexit secretary David Davis, who deemed single market membership "improbable" without migration reforms.
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Launching today with a report on the Single Market, the group is calling for the UK to withdraw, even if no alternative trade deal is struck.
“It is in the EU’s interests to agree a zero tariff deal with the UK simply because it sells more to the UK than the UK sells to the EU.
However if they refuse to do so within reasonable timeframe, the UK should leave the EU without a formal agreement, after Article 50 has been triggered, relying on WTO rules and striking free trade deals with our global partners,” Leave Means Leave said.
“The UK would swap a current marginal influence on Single Market regulation for no say in regulatory framework at all while having to accept free movement of people.”
The group further complains of “needless and expensive” regulation for UK businesses, regardless of whether they export.
Responding to the launch of the group on behalf of Open Britain, formerly the official Remain campaign Britain Stronger in Europe, Anna Soubry said: “The biggest threat our economy faces is Leave campaigners wanting to leave the EU with no trade deal at all.
“This would mean new tariffs on nine out of ten goods we sell to the EU, including 10 per cent on cars. This would decimate our national industries and cost jobs.”