Friend or colleague?

Anyone who has moved city to take a new job knows just how hard it can be to make friends as a grown-up. Agony aunts recommend meeting people by joining sports clubs and interest groups, which is all very well except for the fact that impressing a new boss means working long hours and generally not asking to leave on the dot of 5pm to attend a medieval theatre workshop, no matter how lonely you're feeling.

As a result, it's much more time-efficient to make friends with colleagues. Unfortunately, it can be hard to tell if these are real friendships or mere acquaintanceships of convenience, as occur when actors fall in love on a movie set only to discover that they have nothing in common once they're out of costume.

Here's how to tell if your water-cooler pal will last the distance:

1. Ask him (and his family) to lunch at the weekend. If he's always busy or he counters your invitation with the suggestion that a quick drink at the pub after work might be more fun, he's a colleague. If he says yes - and returns the invitation later - he's probably a friend. If he already knows where you live he might be a stalker.

2. Assess your coffee-buying habits. Friends aren't too fussed about who paid for the last latte because they know it will all sort itself out in the long run. Colleagues are more likely to want to keep track of the cash - they'll pay you back when you buy them a hot drink and expect the same from you in return. It's not rude; it's just neater.

3. Quit. This is clearly a big step to take, and frankly I don't recommend it unless you are planning to take a new job anyway - doing it just to test your friendship is more than a little creepy. Note also that the test isn't related to drunken statements of affection at your leaving do or even to how big a bunch of flowers can be bought from the office whip-round; it's about who you're still in touch with three months after you've left. If you still see them regularly in a social setting, they're your friends. If you only speak to them by phone or at events where people wear suits and juggle canapes, they've become part of your professional network. If you find yourself hanging around your old work local hoping to bump into someone who can reminisce about the good times you had working on last-minute pitches, it's time to find some friends. Maybe you could join a club or take up a sport.