"In our lifetimes we have never seen such a degree of unanimity among economists on a major policy issue. The precise effect, in terms of numerical percentage, is of course uncertain. But that we would be financially worse off outside the EU than in is almost certainly true," the directors of the three institutions said in a joint statement, as quoted by The Independent newspaper.
The directors also cast doubt on the Leave campaign promise that the post-Brexit United Kingdom will be able to trade with European nations on good terms while saving up to 10 billion pounds ($14.7 billion) on public services and tax cuts.
On Thursday, Brits will vote in a referendum on whether the country should remain part of the European Union.