"Comfort is luxury," the French designer Coco Chanel famously pronounced. Years later the legions of stiff-suited accountants are starting agree.

Arthur Andersen is the latest financial firm to encourage staff to ditch their collar and tie in favour of more casual clothes.

But rather than helping employees to relax, it could be having the opposite effect.

The trend towards "leisurewear" in the office began in the 1980s in Silicon Valley.

The idea was to create a relaxed, fun environment where staff were free to express themselves with their clothes - and would therefore be more productive.

Most UK banking firms put their toes in the water with "dress down Fridays", which saw hordes of professionals descending on offices in identical beige chinos.

But now Andersen's staff have been practically ordered to go "smart casual" every day of the week.

Managing partner Philip Randall - who favours grey slacks and an open-necked blue shirt - reportedly said the firm would "talk to" the people who "don't get it".

Cary Cooper, Professor of Organisational Psychology at the University of Manchester Institute of Science and Technology, said the edict would leave many Andersen accountants "stressed out".

"They've always worn this uniform. It's like being in the military," he told BBC News Online. "They've never had to think what to wear before."

It's not dressing down per se which is the problem, he says, but having to think about what is, or is not, suitable office attire - and then find some for every day of the week.

Once employees get used to the idea, "being informal is better for the working environment," said Professor Cooper. But initially, it's a fraught matter.

"They'll be thinking: 'What is appropriate? What if you suddenly have to meet a client? What is smart casual?" he said.

"Well, I mean, what is it? Even I don't know what it really means."

It does indeed appear that Professor Cooper has hit upon a big problem when conservative British offices try to do what the Americans call "business casual".

There have been reports of bewildered professionals turning up in golfing gear and nightclub attire.

One banker even thought a pinstripe waistcoat teamed with a Grateful Dead T-shirt fitted the new dress code.

Female accountants, Professor Cooper adds, have less trouble.

"Women are culturally much more clothes-conscious than men," he said. "They instinctively know what to wear."

Most firms say their "dressing down" edicts are optional. If employees want to continue wearing suits, they may.

But those who don't want to shell out for an entirely new wardrobe of khakis and slacks face another problem, says Professor Cooper.

They may appear "non-progressive" to their colleagues, or - worse - their bosses. "They risk being seen as old and fuddy-duddy," he said.

However, he added that such choices usually turn out to be a kind of illusion anyway.

"These kind of culture changes usually become edicts," he said. "As in: 'You will not dress up, you will dress down'."

Professor Cooper believes that dressing-down is not a mere corporate fad, but the future of industry.

"The internet and financial sector, the biggest growth earners, are very informal industries," he said. "Relaxed dressing is the way it's going to go".

He advised firms who want to go casual, but who hope to ease their staff into it painlessly, to simply issue very clear guidelines on which items of clothing they consider acceptable.

And as for confused accountants getting used to the idea, Professor Cooper advises simply leaving off the jacket and tie - but making sure they are to hand for emergencies.