The UK government's pension reforms, which will oblige all companies to offer staff adequate pension provision from this October, are set to cost the country's top firms £5bn a year if wages are held constant, according to a report out today.

The reforms will eventually see all employers forced to contribute at least 3% of their staff's salaries to pension funds, auto-enrolling all workers who are not currently members of the company scheme. The new duties fall on the biggest firms, those with over 100,000 staff, in October and in staged dates thereafter for firms further down the scale.