Boris Johnson shakes hands with the president of the European Commission Jean-Claude Juncker after striking the last-minute Brexit deal last monthOLIVIER HOSLET/EPA

The Bank of England has downgraded UK growth on the back of Boris Johnson’s Brexit deal.

After three years the economy will be about £14 billion smaller than previously thought as a direct result of the government’s proposed withdrawal agreement and free trade deal.

The downgrade emerged as two Bank policymakers broke ranks and voted to cut rates this month, citing “downside risks from persistent Brexit uncertainties”. Rates were held at 0.75 per cent after the other seven members of the monetary policy committee voted for no change. Markets now expect a rate cut early next year, however.

The Bank’s decision to revise its Brexit assumption during an election campaign is a surprise. Until now, the model it has used since the referendum has assumed…