Prince Charles, reigning clothes horse of the British Royal family, gave an excellent lesson in how to wear a pocket square yesterday at Royal Ascot.

Chaz knows that a well-chosen pocket square gives even the most formal suit a refreshing change in tone, creating an atmosphere of sartorial friendliness.

The knack of choosing a great pocket square is to make sure it works with your tie, and then fold the edges in on top of themselves as indicated by this GQ style guide. If you have to use it - say for example to chivalrously hand it to a lady who has been moved to tears - simply plonk it back in your pocket afterwards, with the messy bit folded inside. And then don't offer it to anyone else.

It's all the fault of the name really, but Chaz knows a pocket square should never be worn, er, square, as it was by actor Jack Fox yesterday at an Armani party. It's knowledge he has handed on to his son, too.

If you want a more formal look, better to ditch the hankie altogether than impose straight lines.