Ground Floor: The late Lord King, former chairman of British Airways (BA), who died last week, once proclaimed: "If Richard Branson had worn a shirt and tie instead of a goatee and jumper, I would not have underestimated him."

You can't entirely blame King for not taking Branson seriously at first - apparently 50 per cent of our initial impression of somebody is based on what they're wearing. People tend to have particular preconceptions on industry dress codes so it's not surprising that a suitless Branson was way down in the pecking order of the late lord.

King was brought in to save BA and he transformed it from a state-owned weakling to a profitable public company. He fought strenuously for the right to retain BA's exclusive transatlantic routes but he was ultimately beaten by Branson.

The battle for control of the routes was bitter and Virgin complained that BA spread false rumours about it, hacked into its reservations systems and harassed employees. King clearly saw Virgin as major competition but, because of the Branson image, competition that could be beaten by his bigger, more formal organisation. In the end, he will probably be remembered more for losing the subsequent court case - in which Branson won an apology, damages and costs - than his transformation of BA.

Even now, many people find Branson's cuddly, over-grown schoolboy image profoundly irritating but they are in awe of a businessman who expanded the Virgin brand way beyond its modest beginnings as a mail-order record retailer in 1970. The recording company was sold to Thorn EMI in 1992 for $1 billion (€830 million) but by then Branson had already become an entrepreneurial folk hero.

There have been plenty of non-suit-and-tie men who've done well in business and, in particular, the airline industry (I don't think I've ever seen Michael O'Leary in a shirt and tie), but there's still a certain belief that someone in a suit is more capable than someone in a jumper.

The raft of new businesses that sprung up from the dotcom era - and which were based on youth and exuberance and a desire to push away the boundaries of the past - made many people re-think the office-wear culture. But the bursting of that bubble suddenly meant a rash of sober suits and ties breaking out all over the place again.

However, a report by the Peninsula HR group claims that workers who can "dress down" in the office are more productive than those who wear more traditional attire. Employers now say that 70 per cent of people wearing casual dress show an improvement in productivity - that's up from 50 per cent in 2000. So it seems that industry is lightening up a little and that it's more acceptable to come into the office in jeans and a T-shirt because you work better.

Meanwhile, in China, dressing down has become government policy to reduce energy consumption by allowing air conditioners to be turned down. Given their insatiable appetite for energy, it's an understandable request. The Chinese are trying to follow the policy but in Japan, where the same request has been made by the prime minister, workers are struggling to comply.

In the eyes of many Japanese, coming to work with an open shirt and without a tie is seen as disrespectful. Employees of the Tokyo Electric Power company have taken to wearing badges that say "please excuse me for being casually dressed".

But for the average person in an office, is it better to opt for casual or formal? I personally preferred to dress casually in the office but wore a suit whenever I was meeting clients. When representing the company to outsiders, I wanted to show a certain level of respect. I think, too, that if you are going to an important meeting and if you want to appear confident, you can't really go wrong with a well-cut suit.

There is a fear in some firms that casual dressing means a lessening of respect but that doesn't have to be the case. The important thing is that casual doesn't actually mean sloppy, although this is something that many first-time employees don't seem to have grasped. A T-shirt is always casual but a sequined T-shirt proclaiming the wearer to be "trailer trash" is just tacky.

Although some companies like to retain formality, flexibility is the key. The first corporate golf outing I ever attended was an almost male-only preserve and took place on the hottest day of the year. I sat in the clubhouse for dinner surrounded by men sweltering in jackets that they couldn't remove until the captain had given his permission and I suddenly knew the meaning of stuffed shirts.

I asked some of my HR friends whether or not their guidelines on office dressing had changed. Most agreed that informality was becoming more acceptable but that there were lines employees shouldn't cross. Ripped jeans and belly tops are generally taboo. They also pointed out that dressing for an interview was completely different to dressing for everyday work and they would expect a greater level of formality then. It's an image-conscious world and at interview you want to project the strongest possible one.

Almost unanimously, however, they were fairly negative on the question of male facial hair.

So maybe all of them would, like Lord King, have underestimated Richard Branson if he'd turned up with his CV.