The UK’s economic performance is projected to be 4% lower fifteen years after leaving the European Union compared to a scenario where it had remained a member, according to the government’s official budget forecasters. This assessment highlights the continuing economic consequences of Brexit. The forecast suggests a significant, long-term impact on the British economy. While the full extent of Brexit’s effects are still unfolding, this report provides a concrete estimate of the economic cost. The findings underscore the challenges faced by UK exporters as they navigate a new trading relationship with the EU. The report does not detail specific sectors most affected, but indicates a broad, negative impact across the economy.