Human beings are masters of self-delusion. Given the right circumstances, for example, it’s possible to convince oneself that consuming two bars of chocolate in one morning won’t make you fat, or that being good friends with your boss means you won’t get fired.

While I cling to the former delusion, it seems plenty of bankers are reaching for the latter.

On a damp evening recently at a rooftop drinking venue near Bank, one mid-ranking structured credit professional told me that his job was safe because a) he played squash with his boss, b) he went drinking with his boss, and c) he was able to have a frank conversation with his boss (which basically amounted to saying he’d rather be fired than do something demeaning like work in the middle office).

A week later, I met another ‘City professional’ in the same place, who was bemoaning the fact that an old mate had stabbed him in the back. The chum had repeatedly reassured the City professional that all was well, before disposing of him and taking all his clients. And this was a friendship that preceded that particular organisation and went far beyond borrowing the occasional stapler.

The truth of the matter is that in a work-related situation, friendships won’t count for much once things like mortgages, school fees, and food-on-the-table are at stake.

This is a recognised phenomenon. Last year, BusinessWeek ran an illuminating article on the phenomenon of so-called ‘frenemies’, defined as ‘a person you spend time with, enjoy talking with, and rely on at work – but you can't completely trust’.

According to BW, frenemies come into fruition because people are warped insecure: when the chips are down, your frenemy will make sure you look bad and he looks good.

If the chips have ever been several feet underground in banking, it’s now. Little surprise, therefore, that the frenemies are out in force.

In a way, this no bad thing: work is a fundamentally transactional affair rather than an opportunity to develop fulsome relationships with other human beings. The frenemy phenomenon is simply throwing a much needed dose of realism into the mix.

As long as you don’t lose sight of this, having friends in the office is no bad thing. Up to a point, it may even help to save your skin – the banker I spoke to was one of only six people left out of an original team of 13.

However, the moment his boss has to choose between himself or his buddy, or even between his buddy and a blatantly better member of the team, you can bet that friendship will prove as illusory as a low carb bar of chocolate. It's far better to acknowledge this up front.