Image copyright Getty Images

Employers should allow staff to work flexibly and have a relaxed dress code during this week's UK heatwave, the Trades Union Congress (TUC) has said.

Temperatures are set to top 35C and TUC general secretary Frances O'Grady said: "It's in bosses' interests to provide a cool and comfortable work environment."

The TUC wants people to be able to travel at different times or work from home and wear more casual clothing.

It adds staff should have breaks often and cold drinks should be available.

Ms O'Grady added: "While many of us love to see the sun, it's no fun working in a baking office or a stifling factory.

"Bosses should do all they can to keep the temperature down. Nobody should be made to suffer in the heat for the sake of keeping up appearances.

"Workers who are unable to dress down in lighter clothing, or who work in offices without air-conditioning, fans or drinking water, are going to be tired, and lack inspiration and creativity."

There are no laws in the UK about when it is too hot to work, but the TUC would like that to change.

It wants the introduction of a new maximum indoor temperature, set at 30 degrees - or 27 degrees for those doing strenuous jobs - with employers obliged to adopt cooling measures when the workplace temperature hits 24 degrees.

Fitting in with your peers

Despite the TUC's call for staff to be allowed to dress more casually, is this practical in all workplaces?

It very much depends on the organisation where you work, says H&M Group behavioural psychologist Prof Carolyn Mair.

Vest tops and skimpy dresses may be fine for more progressive industries such as technology, but not appropriate for traditional financial services firms, she says.

People wear certain clothes as a way of fitting in with their peers, and as a way of signalling that they identify with the aims of colleagues, she says.

"What we wear is very much a part of our identity," Ms Mair says. "It's a way of saying: 'We expect you to behave in a certain way.'"

But dress codes can be seen as a form of social control, she says.

"The idea is to create uniform behaviour, as well as a uniform look."

Image copyright Getty Images Image caption Could ditching the office dress code make you more productive?

Personally, she is "not a fan of uniforms at all", but for some people, they work, as they make it easier to get out of the door in the morning.

"Lots of women have a wardrobe explosion before they go to work," she says, as they search for the right outfit, discarding certain clothes if they are inappropriate for a particular meeting.

However, being able to wear your own clothes to work "shows your individuality", she adds, and depending on your personality, it can aid productivity.

"For people who really want to be individual, wearing a uniform just isn't helpful," she says. "Being able to choose what they wear is a better way of showing their identity."

Health and safety

That kind of flexibility isn't always possible, says employment lawyer Vanessa Bell, a partner at Prettys Solicitors.

She warns that health and safety always comes first, pointing out that a building site, for example, is likely to insist on protective footwear.

An office is more flexible, but she warns that "employees need to be aware of the dress code or they risk being disciplined".

Image copyright Getty Images Image caption Employers must be careful about sexual discrimination when they dictate dress codes

What employers need to be particularly careful about is relaxing dress codes for women in warm weather and not for men, she adds.

"If [male] employees in customer-facing roles have to wear a suit, a tie, and a long-sleeved shirt", while women can "wear summer dresses and lighter clothes, you have to be careful there".

Doing that opens employers up to sexual discrimination claims, she says.

Image copyright Getty Images Image caption Virgin recently relaxed its dress code for flight attendants

Many firms have recently relaxed their dress codes, including major banks such as Goldman Sachs and JP Morgan, whose staff have typically always worn suits.

Goldman announced the "firm-wide flexible dress code" earlier this year, urging employees to use "good judgement" in their fashion choices.

In March, Virgin Atlantic also said it was relaxing its uniform requirements for cabin crew, saying they no longer had to wear make-up while on duty. It also said females would be automatically offered a choice of trousers as well as a skirt.

What are you expected to wear?

But when the BBC asked people on LinkedIn how flexible their firms were on dress, many said their employers still took a traditional approach.

"Last year when I was with my old company, when we had the heatwave, everyone still had to come in shirt, tie, trousers and shoes, it was boiling!" says Jason Sweeney, a business developer at Yorkshire-based graphic design company Prime Creative.

"Saying that, I now work in a office where we have casual Fridays, and if it's hot you can dress for it. It's a much better way to work, allowing employees to be comfortable."

Andrea Philippou, a web researcher at IT firm Digicert, said firms needed to "prioritise humanity over the superficial corporate 'uniform' image".

"I am not saying that it should be acceptable to walk into our work environment in our pyjamas without showering, but to accept that people can still accomplish great things without having to wear an Armani dress or suit every day," she added.

Image copyright Getty Images Image caption Many law firms are implementing casual dress

Leanne Lawrence, an associate solicitor at Lodders Solicitors, says her firm has started to allow people to wear casual business dress every Friday.

"On the whole, I am hearing that a lot of law firms are starting to implement some type of casual dress policy, although with law firms and other service industries, I feel that external perception can sometimes be an issue.

"I feel that casual dress can increase productivity and I personally often save heavy drafting days for those casual dress days when I feel more comfortable.

"I am aware that others still feel slightly uncomfortable with the concept and often it is difficult for staff to understand what is 'office-appropriate' dress down. I guess it depends on your personal opinions, but it is nice that at least employers are starting to give staff the choice."