Gordon Brown’s pledge to cut the red tape burden imposed on business by £4bn, and increase productivity by up to £16bn, is based on numbers that are probably “overcooked” and cannot be relied on, the National Audit Office has warned.

The £4bn target is a central plank of the prime minister’s commitment to tackling red tape. All Whitehall departments have been required to draw up “simplification plans” to meet the target by 2010.