Almost two decades after the collapse of US giant Enron in a notorious accounting scandal, the accountancy sector is back in the spotlight, this time thanks to a string of scandals in Britain.
The sector's so-called "Big Four" Deloitte, EY, KPMG and PwC have a long-established oligopoly to advise and monitor big business, experts say.
The powerful companies engage in a wide range of activities, from accounts auditing and strategy consulting to proposed mergers and acquisitions, restructuring and taxation.
However, a series of high-profile corporate collapses in Britain including retail giant BHS in 2016 and construction company Carillion in early 2018 have put them into the crosshairs of the authorities.
The Competition and Markets Authority watchdog launched a sector review in October and is expected to report back before Christmas.
- Firms need them -
Despite the controversy, firms feel they need one of the Big Four on their side as investors usually want to see their labels when they scrutinize the quality of companies.
"Firms need to placate financial markets and having a 'Big Four' badge is one easy way to do this," Professor Crawford Spence at King's College London told AFP. "These symbolic aspects are very important."
The Big Four audit all but one of the 100 companies listed on London's benchmark FTSE 100 stocks index, media reports say.
"This is partly explained by the need for big listed companies to have an auditor with an international network who can deal with subsidiaries overseas, partly with issues to do with brand," added Spence.
"The Big Four ... pride themselves on trying to understand the whole business of a client, not just its audit issues. This 'rounded business knowledge' is very useful for big clients."
Yet the sector has seen its reputation tarnished in recent years, despite changes enacted since Enron's collapse in 2001, which experts say was probably the world's biggest accountancy scandal ever.
The Financial Reporting Council, which oversees the industry, fined PwC a record £6.5 million in June over auditing failures of BHS, two years prior to its collapse.
- 'Toothless' -
KPMG meanwhile faces a FRC probe over its audit work for construction group Carillion, which went bust in January, amid concerns it may have breached ethical and technical standards.
The FRC -- which stands accused by a British parliamentary committee of being "toothless" -- has also proposed a series of reforms for the troubled sector.
They include a possible ban on accountancy groups earning lucrative consultancy fees from companies that they also audit.
However, Professor Spence argued this would fail to address the broader issues -- adding that the quality of audits must instead be improved.
"The key issue here is auditor independence. As long as management appoints and pays for auditors themselves, the same conflicts of interest will keep resurfacing.
"What is needed are auditors to be appointed by panels of shareholders or other stakeholders."
He added: "Competition is a red herring here. If you look at other countries where they have tried to do something about Big Four monopolies, the effects have not been particularly inspirational.
- 'Perverse effects' -
"In France, the state forced companies to appoint joint auditors – this had the perverse effect of increasing the concentration of the audit market even further."
The Big Four also have more than 95 percent of FTSE 350 businesses on their books.
In reaction to their strong grip, Grant Thornton -- Britain's fifth biggest accountancy firm -- announced in March that it would stop bidding for new auditing contracts as it could not compete.
Yet Grant Thornton itself has also found itself at the centre of controversy.
The FRC this week announced a probe into its audits of British cafe chain Patisserie Valerie, a client of Grant Thornton, which came close to collapse last month after uncovering a black hole in its accounts.
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