Britain’s budget watchdog said a hit to the economy from leaving the European Union is unfolding as it expected, maintaining an outlook that Brexit supporters have criticized as overly pessimistic.

The Office for Budget Responsibility on Wednesday said its long-running prediction is “broadly on track” to show a 15% fall in trade and a 4% reduction in the UK economy’s potential productivity compared to if the UK had stayed in the EU.

The institution charged with assessing Treasury policy was attacked by some right-wing lobby groups and members of Parliament for being overly downbeat on the UK’s prospects outside of the trading bloc. Brexiteers accused official forecasters of exaggerating the possible impact of a UK departure in the run-up to the vote.

However, the OBR’s analysis chimes with that of the Bank of England by showing that a long-term squeeze on the country’s economic potential from Brexit is playing out as they feared.... m