Hardline Brexiteers have demanded Theresa May walk away from Brexit talks if the EU refuses to discuss future trade before Christmas.

MPs and others in the Leave Means Leave group penned a letter to the Prime Minister saying she should call the EU’s bluff and drop negotiations if Brussels does not allow progress.

Brexit talks are currently progressing at a snail’s pace, with Ms May’s speech in Florence having brought some momentum but the EU still insisting Britain settle its financial obligations, guarantee EU citizens’ rights and properly address the Irish border issue before any trade deal is discussed.

It comes as Boris Johnson also set out his redlines for Brexit, further aggravating cabinet tensions, while Scottish Tory leader Ruth Davidson called for “serious people” to take charge of Brexit.

The Leave Means Leave group stated in its letter: “If the EU is not seriously negotiating a free trade deal by Christmas 2017, the Government should give formal notice that we will move to World Trade Organisation rules in March 2019.”

Signatories calling for the hardline stance include former Brexit minister David Jones, and the issue is set to feature heavily at the Tory conference.

Leaving with no deal as they suggest would mean high tariffs on both EU and UK goods, with more moderate members of the Conservative party warning it would be a catastrophe for the economy.

Mr Johnson also used his interview with The Sun to clearly set out his Brexit redlines, which constrain Ms May’s position and further strain tensions with other ministers like Philip Hammond and Ms Davidson seeking a more jobs- and economy-focused Brexit.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

With the Foreign Secretary recently having hailed Britain’s “glorious” future outside the EU, Ms Davidson used an interview with The Times to call for serious people to take charge of Brexit.

As the party faithful converge on Manchester, the Prime Minister insisted Labour was “unfit to govern” as she pledged to listen to the concerns of young voters after the Tories lost their Commons majority in the snap general election in June.

Ms May said: “As Conservatives, we have a vision of a country that works for everyone, not just the privileged few – precisely the direction I set when I became Prime Minister last year.

“I understand the concerns raised, particularly by young people, during what was a disappointing election for my party.

“So my determination to act on those concerns, and crucially, to fulfil the promise of my first speech on the steps of Downing Street, is greater than ever.”

Ms May added that the conference would see the party “setting out our road to a better future for you and your family”.

She said: “Yes, we have to get the best Brexit deal – but we must also take action here at home to make this a fairer place to live for ordinary working people.

“The social contract in our country is that the next generation should always have it better than the last.