Theresa May refused to be drawn over whether she favoured Britain’s continued membership of the single market on Wednesday

Ministers are accused by Britain’s former trade boss of being excessively optimistic about their ability to conclude new deals with major world economies.

Sir Andrew Cahn, the former chief executive of UK Trade and Investment, said claims by Liam Fox, the trade minister, that the government could have a network of deals ready to be signed by the time Britain left the EU were “highly unrealistic”. Even comparatively simple agreements would take at least two years to negotiate, he said, a process that could only start when Britain’s economic relationship with the EU itself had been resolved.

Sir Andrew added that deals with major economic powers such as the United States and China would take much longer — at least a decade. He pointed out