Thr Royalist was always taught to stand up and offer one's seat to a pregnant lady when on public transport, but there's a problem.

How do you tell if the woman in question is pregnant, or just fat?

When Kate Middleton took a short trip into London's subway with her grandmother-in-law the Queen today, she  was given a 'baby on board' button that pregnant women are encouraged to wear on the tube so that true gents who wish to leap up and offer their seats are able to do so without risking the grave offence of offering one's seat to someone who isn't with child.

London Underground's chief operating officer Howard Collins who presented Kate with her 'Baby on Board!' button, told the Daily Mail:  "I said they're fantastic, they really do make a difference - saves men the embarrassment of having to guess if a woman is pregnant. She asked so many great questions of the staff and seemed really interested our work."

Kate wore a teal Marlene Birger coat dress for the outing with the Queen, who appears to be finally recovering from the flu bug with which she was hospitalised.