The OBR has caught some flack from pro-Leave Conservative MPs over its economic forecast of more government borrowing and reductions in economic growth after the Brexit vote.
MP Jacob Rees-Mogg is among others who have said the Office for Budget Responsibility is wrong in its predictions because its calculations assume that the UK will maintain the existing trade tariffs when Britain leaves the European Union.
However, OBR chief Robert Chote tells Today that it can only work on the basis of the "information we’ve got at the moment".
“We’re being slightly more optimistic than the average of outsiders at the moment," he says. "There are people who think we’re being not optimistic enough, there are people who think we’re being too optimistic. We need the policy [on Brexit] to clarify itself; we also shouldn’t delude ourselves that it’s going to clarify itself very quickly.”