Conservative Brexiteers plan to challenge Theresa May directly by publishing their own “positive” blueprint for a hard Brexit.

Work has begun on a policy paper, due to be published next month, outlining the advantages to Britain of leaving the European Union on World Trade Organisation terms. It is expected to have the backing of 60 to 80 Conservative MPs, increasing the pressure on the prime minister before the party conference in Birmingham.

Although the paper is still being developed it is understood to allow for a possible Canadian-style free trade agreement, but only if the EU backs down on demands over the Irish border. If the EU refuses, the paper will say, Britain could thrive by relying on WTO mechanisms.

Under a Canadian-style agreement,