You have to judge things ooh so finely on the tube: know where to stand to get a seat, know which carriage is the nearest the station exit, and of course, just what to do if a pregnant looking woman enters.

The latter is the hardest, there's a series of internal questions that need to be worked through: are they really pregnant when a seat is really what they want, (or may not - one heavily pregnant woman once thanked me for offering up my seat, but " ..if I sit down then I'll never get up again, so I'll stay standing but thanks anyway..."); or are they actually overweight and don't want attention drawn to that; then again, could it simply be a case of bulky clothes, how the folds drop and so on, so they seem pregnant but they're actually not.

Let's skip the wheat from the chaff sorting and look at what happens on the tube, what's the reaction? Usually there's a man rising and then a pregnant woman settling a few moments later on to a warm tube seat.

But the experience is n't as straightforward, there are variation, different tube lines seem to have different approaches. District line trains rolling in from genteel west London usually have a brace of elegantly attired suits slipping off their seats and offering them up with a flourish and a steadying arm; the Hammersmith and City can be a sulkier line in many ways, a creative, bohemian sulk by the way, artist in extremis sensibility, but once they've pushed their shades down and twigged there's a mum to be rocking on both feet and looking weary, then they'll pop out of their seats and point to the free space. No words, gestures only. Central Line, my favourite; the moment, the very instant a pregnant woman steps into the carriage, men zoom out their seats like a row of champagne corks going off. Even if she only had sex last night and the egg's still busy fertilising, Central Line men just seem to know.