Unilever is looking for a new auditor, after 26 years with PwC, to comply with a new rule, prompted by questions over why accountants gave banks a clean bill of health just weeks before they were rescued by taxpayers in the 2008 financial crisis.

Britain's Financial Reporting Council (FRC) said last year that companies should consider changing their auditor at least every decade in order to end cozy long-term relationships.

Only a few blue-chip companies have taken any action so far.

HSBC , a KPMG client since 1991, has said it will put the work out to tender - the only bank to do so.

Barclays has yet to consider a tender, having used PriceWaterhouseCoopers (PwC) for the past century, Royal Bank of Scotland has been with Deloitte since 2000, and PwC has audited Lloyds' books for about 140 years.

Asset manager Schroders has just retendered but had to stay with PwC after discovering that appointing KPMG would breach conflict of interest rules. KPMG has also just replaced Deloitte as auditor for insurer RSA .

Change is costly and time-consuming and used to occur only because of disagreements between auditor and client.

A UK Competition Commission investigation found that almost a third of top 100 companies have had the same auditor for more than two decades. The "Big Four" - PwC, KPMG, Deloitte and Ernst & Young - audit most of the top firms.

"To maintain Unilever's position at the forefront of good governance, we have decided to put our statutory audit work out to tender with the intention of nominating a new external auditor for 2014," Unilever Chief Financial Officer Jean-Marc Hu��t said in a statement.

Melanie McLaren, the FRC's executive director for codes and standards, said the rule was beginning to prove itself and will urge the Competition Commission to hold off for the time being.

But the Competition Commission proposed on Monday that top companies should put their book-keeping work out to tender every five years, a significant hardening of the FRC initiative.

And the European Union is approving a draft law that is likely to go further and force an actual change in auditor.

Another criticism is that some companies are so big that tendering will see the Big Four swapping customers rather than giving smaller auditors a chance to have a piece of the pie.

(Editing by Louise Ireland)