KPMG could lose the biggest audit contract in corporate Britain after HSBC decided to consider bringing in a fresh pair of eyes to vet its accounts.

The bank said it would put its audit contract out to tender for the first time in more than two decades in the most striking sign yet that regulatory pressure is starting to break down the ties that bind many big companies to their auditor.

HSBC paid KPMG $81m in 2012. The majority of this was for audit and audit- related services, the rest being tax and other consultancy work. It has held the audit contract since 1991.

In a recent ranking of FTSE 100 audit contracts, Accountancy magazine classed HSBC as the most lucrative assignment, just above Barclays and well ahead of Royal Bank of Scotland, Lloyds Banking Group, BP and Royal Dutch Shell.

The tender could give KPMG rival Ernst & Young an opportunity to pick up a big British bank as an audit client. HSBC said it wanted the winner of the tender to be in place by 2015.

If HSBC were to drop its long-time auditor, it would be following in the footsteps of Schroders, the fund manager, which earlier this year ended a relationship with PwC stretching back more than half a century. KPMG was hired instead.

Other FTSE 100 groups to announce an auditor switch in recent months include RSA, the insurer, and BG, the energy group.

The rush of activity has come with the audit market in the UK under intense scrutiny in the wake of a Competition Commission investigation.

In addition, the profession is still trying to dispel lingering dissatisfaction with its failure to warn investors of imminent bank failures during the financial crisis.

The Competition Commission last month proposed that big companies should be obliged to put their audit out to tender as frequently as every five years, while also mooting the idea of forcing companies to switch audit firm periodically.

Investors are concerned that an audit firm loses its independence if it is in place for years on end, even though lead audit partners are regularly rotated.

The measures put forward by the Competition Commission are more aggressive than the position taken by the lead accounting regulator, the Financial Reporting Council, which encourages groups to re-tender at least once a decade.

HSBC said its move was prompted by the FRC’s recently adopted stance.

KPMG declined to comment.

Banks are the most complex entities to audit, making it unlikely that any firm from outside the four biggest – PwC, Deloitte, KPMG and Ernst & Young – would put themselves forward to audit HSBC’s accounts. (By Adam Jones at Financial Times)