This image is just how the Big Four accountancy firms like it, not least because it hides what they really are – the handmaidens of greed, graft and crony capitalism.

Deloitte, KPMG, Ernst & Young and PricewaterhouseCoopers are supposed to be the guardians of good business but have become the pin-striped promoters of the worst corporate practices.

They signed off the accounts of the banks which collapsed, failed to raise the alarm over BHS and Carillion and helped firms avoid tax on an industrial scale.

If you want to know why capitalism has such a bad reputation you need to look at the very people supposedly responsible for policing it.

It was not always like this. When the big four started, they were simply auditors.

But the deregulation after Thatcher’s “big bang” in the 1980s saw banks turn to ever more inventive ways of making money.

They could bundle up debts and sell them on, and bet against how much money that would make.

Instead of loaning money to firms, the banks started buying them. Instead of investing, they speculated. And the accountancy firms wanted a slice of this action.

In addition to auditing, they started offering consultancy – often to the firms whose books they were meant to be checking.

Nobody seemed to care about this blatant conflict of interest… until things went wrong.

Take the collapse of Carillion, which went bust with debts of £7billion.

Ten months earlier, KPMG had given its financial statements its seal of approval.

Since 2008, KPMG had received £20.2million in fees from Carillion.

In the same period, Deloitte netted £12million and Ernst & Young £18.3million.

The real winner, though, was PwC – which banked £21.1million from Carillion and is expected to make £50million overseeing its liquidation.

MP Frank Field accused the accountancy firms of “feasting on the carcass” of the firm.

Defenders of capitalism like to claim it encourages competition but this does not appear to be the case when just four firms have a near monopoly of the market.

In the UK, they audit 341 of the 350 biggest listed companies. And why go elsewhere when you can hire firms apparently willing to sign off accounts at the stroke of a pen and bag a lucrative consultancy contract at the same time?

A PwC auditor signed off BHS’s accounts days before it was sold by Sir Philip Green after spending just two hours looking at files. An internal note suggests the worker backdated his audit and failed to gather evidence on “whether BHS was a going concern”.

Then there is Lehman Brothers, Northern Rock, HBOS – all deemed going concerns by auditors shortly before their collapse.

In 2007, PwC’s audit of Northern Rock concluded “that in our opinion there were no matters relating to the going concern … that were required to be reported to shareholders”.

The bank’s ­collapse a few months later cost the taxpayer £2billion.

PwC later said it was not the “job of the auditor to look at the business model of a business”.

The Big Four also stand accused of advising big firms and high net worth individuals on how to stash cash away in tax havens.

The Paradise Papers showed Ernst & Young helped F1 champ Lewis Ham-ilton set up an offshore structure to avoid paying tax on his private jet.

Members of the Big Four have also faced accusations of misselling, turning a blind eye to bribery and collusion in corporate fraud.

Instead of questioning such behaviour, the Government rewards them with lucrative deals. Since 2015, the four firms have bagged Government contracts worth £1billion.

The Commons Business select committee has now launched an investigation into the Big Four and whether they should be broken up.

Chair Rachel Reeves said: “The audit market is broken. The Big Four’s overwhelming market domination has failed to deliver audits which are fit for purpose.”

Regulation is so lax we have no idea how much an auditor charges or how long they spend looking at the books.

Prem Sikka, emeritus professor of accounting at the University of Essex, says reforms are needed.

“The quality is low, competition is non-existent and the regulation is poor. It is almost impossible to sue negligent regulators in this country. To this date not a single accountancy firm has been investigated, prosecuted, fined or disciplined for selling tax avoidance schemes even though some of those schemes are unlawful.”