Theresa May’s promise to make the UK one of the “great trading nations” after Brexit has been cast into doubt after official forecasts predicted EU uncertainty would suffocate exports for a decade.

The Office for Budget Responsibility signalled that the country is facing ten years of sluggish trade in contradiction to Brexiteer claims that Britain can quit the EU in 2019 and sign quick lucrative trade deals.

In its Economic and Fiscal Outlook the OBR said its central forecast assumes, “that the negotiation of new trading arrangements with the EU and others slows the pace of import and export growth for the next 10 years.

“We have calibrated this on the basis of a range of external studies of possible trade regimes.”

OBR experts said the impact on the economy of slower export growth would not be great, because it would also be balanced by slower import growth.

But the prediction challenges the Government’s claims that the UK will shed its EU membership for a role as an outward looking, trading country.

UK: Theresa May lays out post-Brexit plan at party conference

Ms May used her first Cabinet meeting in September to tell ministers how Brexit would give the country the chance to become one of the “great trading nations in the world”.

Similar Rhetoric has been repeated by International Trade Secretary Liam Fox, Foreign Secretary Boris Johnson and Brexit Secretary David Davis.