How many friends do you have? Not acquaintances. Or spacebook pals. But proper mates: people who would still come to visit if you swapped trading exotic derivatives in the City for a part-time job flogging hot tubs in Wolverhampton.

It’s a question we all ask ourselves periodically – usually at 3am, after a bottle of Bombay Sapphire – though when I considered it recently I was taken aback by the answer. Not because the number was so low. At eight mates, I have, according to a recent survey, the average number for someone just out of their twenties. But because several people who would have made the cut last year – colleagues at my then employer I regarded as pals for life – no longer did so.

The revelation made me feel guilty until a conversation with some new colleagues made it evident that shedding workfriends was par for the course. One said he had accumulated just two lasting mates over nine years at two preceding workplaces. Another said she had not retained a single real friend over eight years at four preceding workplaces. It seems friendship is eternal, unless you meet at work, in which case it lasts until the moment you are escorted out of the building by security.

Why is this the case? On reflection, I think there are three factors at play, the first of which is the simple reality that work friendships, though they don’t feel like it at the time, tend to be shallow. As with family members, you don’t get to choose your colleagues, and the things that bring you together are usually not profound: office politics; necessity; gossip; bitching; drinking; a shared predilection for Drifter bars. And when work is taken out of the equation it can quickly become apparent that you actually have nothing in common.

The second reason why work friendships rarely survive a career move is that, for the friends you have left behind, you are the epitome of their failure and/or paralysis. It’s shaming, but envy plays a role in most friendships – We Hate It When Our Friends Become Successful, as Morrissey sang – but inevitably plays a particularly big role in work relationships as success is so valued in office culture. And even if they are not envious, even if your new job is a demotion, they may still find your departure psychologically traumatic, for you have weighed up the pros and cons, and decided friendship is not enough to keep you at the company. Such rejection can be hard to take.

Conversely – and this is the third reason why workplace friendships are so hard to sustain – you may no longer want to see your former workmates because they epitomise the uncomfortable fact that you are dispensable. At some level, no matter how well adjusted you are, you want your former employer to collapse without you, to come begging for your return on a daily basis, but seeing your cheerful former colleagues is a reminder that everyone is getting on fine without you. There is an analogy to be made here to romantic relationships. You may have ended an affair, and want the other person to be happy, but you still don’t necessarily want to hear about what a great time they’re having without you. To some degree, you want them to be eternally bereft, permanently pining for you.

So does all this mean workplace friendships aren’t worth the bother? There are certainly people out there who subscribe to the adage that business and friends should never mix. Numerous self-help books advise avoiding friendships at work on the grounds that they raise the risk of being gossiped about, create drama and cliques, and distract you from the task of actually getting some work done. Incredibly, some companies even have “nonfraternisation” policies that prohibit employees from having friendships beyond the workplace.

However, other companies go out of their way to encourage fraternising, designing offices to encourage employees to congregate and putting on events to encourage them to socialise. There is evidence to suggest they are wise to do so. Various studies have shown that having friends at work lowers staff turnover and increases safety, productivity and customer loyalty. Moreover, many employees view friendship as a perk: asked to choose between having a best friend at work or a 10 per cent pay rise, in one recent survey, the friend won out among respondents.

Indeed, I think workplace friendships are always worth cultivating. We spend most of our life at work, and anything that makes that time more pleasurable is precious. And anyone who says that such relationships are not really friendships – some experts go as far as suggesting they should be renamed “colleagueships” or “workships” – does not really understand the nature of friendship.

Yes, “workships” tend to be shallow, but friendships don’t need to be deep to be valuable. We get different things from different people. Some mates are mates because they are lovely people, brilliant advisers, and share our values. Others just make us laugh, or put on cool parties, or have a holiday cottage in Tuscany. A friendship based on work is no less valid.

And so what if doesn’t last? I interviewed Julie Burchill some time ago and remember being horrified when she remarked it was necessary to dispose of pals periodically. “Friends are forever!” I thought, recalling what I think is a line from The Care Bears Movie. But having grown up a little since then, having dumped some friends and been dumped in return, I realise she was right. Just because a relationship doesn’t last doesn’t mean it was not worth pursuing in the first place. Besides, some workmates do survive all of the above – I am fortunate in having a couple that have done – and when they do, they are worth their weight in derivative contracts

Read Sathnam's blog posting on this topic on Snakes & Ladders

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