Take off that jacket, sir, and chill out

Strange things happen to the dress sense of the British workforce during the hot summer months of July and August. Traditionally the time of year when cab drivers take to wearing madras check bermudas, peach polo shirts and state-of-the-art sunglasses, it is also the cue for even the most sober-minded workers to abandon their normal office dress codes and lurch from the sublime to the ridiculous.

We are at heart a dark-suited nation - fine in the winter under the heavy camouflage of wool suits and sober colours, but at a loss in hot weather. As soon as the mercury starts to rise, standards can be seen dropping on an almost weekly basis. And whereas 30 or 40 years ago office workers conformed to a strict dress code come snow or stifling heatwave, today it is all much more confused.

For women, the definition of suitable office attire now encompasses casual printed slip dresses over tight-fitting T-shirts; long floaty dresses with beach shoes; and pastel-coloured shift dresses which leave the arms completely bare - hugely popular with women of all ages. It's a far cry from the plain, tweedy skirt suit and crisp blouse combo that was the only appropriate office wear in the 1950s. Similarly, while 30 years ago men would no more wear a pair of shorts to the office than they would a Hawaiian shirt, in many creative, advertising and media jobs a pair of shorts or casual trousers is today perfectly acceptable.

Employers it seems, are increasingly willing to relax the rules. "Our staff are required to wear ties from 1 September to the end of May, but not during the summer months," says Andrew Ford of London Central buses, while on other bus routes managers turn a blind eye to drivers and conductors wearing shorts and deck shoes.

White-collar workers are also benefiting from a more enlightened attitude. Several US companies, including Chase Manhattan bank and American Express, have paved the way with a liberal "Friday dressing" philosophy. Employees are allowed to abandon formal office attire for one day a week on the principle that morale goes up and people are more productive if they feel comfortable in what they are wearing.

But there is a danger that the further you drift from normal office conventions, the more you undermine your air of authority. It is hard to command respect if your clothes suggest you would rather be sipping cocktails at a beachfront bar in St Tropez. "In extreme cases, it is possible, in two months, to erase office credibility that has taken years to build up," says the image consultant Mary Spillane. "Generally, the higher up the ladder you are - or the more you care about your career prospects - the more you should conform to a dress code."

The code varies greatly according to the culture of the workplace. City men and those in legal professions, for example, daren't bend the rules beyond opting for a suit in a lighter-weight fabric or a slightly more colourful tie. "Flamboyant dressing is still frowned upon in the City as a sign of egotism and rebellion," says Richard Rawlinson, deputy editor of the trade magazine Fashion Weekly. Men in the media and advertising professions, by contrast, often consider themselves smart in an open- necked shirt, chinos, or casual trousers and jacket.

Women appear to have it easier, but for them the problem of summer dressing is compounded by the options available. It is very difficult to feel comfortable in the tightly fitted suits, high strappy sandals and red lipstick currently prescribed by top fashion magazines, but the serious executive woman would still think twice about casting aside her neat suit and polished image in favour of crumpled linen layers or a puff of chiffon - even if such unconstricting clothes are more comfortable.

"My only concession to summer is to wear a short-sleeved shirt as opposed to a long-sleeved, double-cuffed, man's-style shirt," says Penny Scott, assistant director of corporate finance at Hambro. "I wear suits identical in cut and design to those that I wear in winter, although I might choose a paler colour, such as off-white, and a lightweight fabric like linen."

There are certain rules, according to Mary Spillane, which women should heed, however high the temperature soars. Bare legs and armpits and naked feet are all high on her list of office no-nos. "Exposed feet and painted toe-nails poking out from open-toe shoes are just too sexy," she says. "Lingerie visible under semi-sheer clothes is also very inappropriate and provocative. The fact that women wear less underwear in summer can be incredibly distracting for male colleagues. London Underground, for example, is just a mass of bottoms and breasts jiggling under flimsy fabrics at this time of year."

Donna Karan, the American designer who pioneered formulaic dressing for working women, prescribes "layering" as the smart solution to the demise of the Eighties power suit and loosening up of dress codes. "It's fine to work at your PC in a sleeveless shift dress so long as you always have a jacket handy in case you are called into a meeting," she says. Layering, she adds, also gets round the vexing dilemma of air conditioning whereby you dress in the morning for stifling heat and then freeze in your fridge-like office.

For men, a major pitfall is their inability to differentiate between a summer and a winter wardrobe. "Often it's because they are too economical," says Richard Rawlinson. "Whereas continental men appreciate the need for suits for both seasons, Englishmen wear winter suits all year round. With advances in fabric technology - 'cool' wools, for example - there really is no excuse to see a hot, sweaty businessman in heavy flannels, red in the face and mopping his brow."

The stiff-upper-lip approach - stoically turned out in double-cuff shirts, worsted wool suits and heavy brogues - might still be welcomed in some professions. But employers are increasingly chilling out. It is not yet a case of anything goes, but there is certainly a lot less to get hot under the collar about.