Lehman Brothers, the American investment bank, has sent a memo asking all staff to turn up in suits. It was the first to encourage employees to emulate the casual dress favoured by so many of its up-and-coming clients during the dotcom boom of the late 1990s. Many other companies adopted 'dress down Fridays' or 'mufti' days. But now men are asked to wear suits and ties, while women will have to wear a skirt, trouser suit, dress or 'other equivalent attire' when the new rules come in on 11 March.