Simon English: Goldman Sachs has to change its ways fast in a new reality or face relegation

Outlook: Investment banks are like football clubs. At some point they fall. Always. This event often occurs at, or shortly after, the point at which they seem most invincible. There is no such thing as a fail-safe investment bank. Just one that has not failed yet.

Goldman Sachs has had a terrific run (for itself, anyway, clients are perhaps less certain).

Is that run now over?

It could be.

The reason the letter from Greg Smith to the New York Times is so devastating is that it speaks to every critical rumour that has done the rounds about Goldman Sachs since at least 2006.

It bets against clients as a matter of routine. It has zero compunction about making a dirty dollar today – tomorrow can look after itself.

The top bankers are arrogant, insular and unruly.

Even if this is a bit unfair, the perception grows.

Five years ago, if you asked the chief executive of a FTSE 100 company why he hired Goldman, the answer might be: because they are the best and the brightest and because I need their advice. I can't be without them.

Two years ago, the answer was: because I've always used them, they know so much about us I don't want them working for the opposition.

Now it might be: I don't know why we still employ them. We should hire someone else.

If one big client goes, another follows. Like advertisers at The News of the World as the phone-hacking scandal broke.

Goldman's franchise is severely damaged. It is hard to see how it can recover its reputation without a major overhaul, including at the very top of the firm.

It has been fined by regulators, sued by clients and become a byword for greed in the financial sector. Some of its staff may go to jail.

One of the myths perpetuated by and about Goldman is that everyone who works there is some sort of erudite, smooth, intellectual genius.

I kicked around for a little while with three Goldman guys in New York years ago. They were tremendous company (in short doses). And utterly full of themselves. And usually smashed after 9pm.

By their accounts, they excelled at their jobs for "the firm" (that's what they called it. It was supposed to be bad luck to say the name out loud in public. But it just sounded cocky).

Even assuming they were brilliant, they were brilliant in one direction only. Their cleverness at trading extended into no other fields.

The boss in London, Michael Sherwood, is an extremely sharp man. He's also on the brusque side of direct, shall we say. He's always understood that the press (and everyone else) will do what he says, take his word as gospel, for the simple reason that he's from Goldman Sachs. No further questions necessary.

The entire firm is so used to (nearly) everyone being desperate to be its friend, it may struggle to cope with what may be a new reality. David Cameron is suddenly wishing he hadn't been pally with Rebekah Brooks. Goldman clients are going through a similar thought process.

How much trouble is Goldman Sachs in?

Don't expect a Lehman Brothers style implosion, but the firm is in the fight of its life.

It needs to change fast and clients need to believe that it has done so.

Otherwise relegation awaits.

Goldman Sachs. News International. Manchester United.

The football club is currently top of the league. Goldman is still in the top four.

But empires fall. Always.