British workers should be allowed to swap ties and jackets for shorts and T-shirts during Britain's heatwave, a union group said today.

The Met Office this week issued a heatwave warning, the first for three years, saying temperatures would soar to about 33 degrees Centigrade in London tomorrow.

The scorching weather prompted the Trades Union Congress (TUC) to urge employers to adopt a more relaxed approach to office attire and uniform requirements.

"The TUC believes that the best way for staff to keep cool inside when it's swelteringly hot outside is for them to be able to sport less formal, more casual clothing, and come into work in shirt sleeves and shorts," the union said in a press release.

"We'd like British bosses to think seriously this week about how they can make their workplaces cooler and their staff less overheated," TUC general secretary Brendan Barber added.

The union said it understood that vests would not be appropriate for workers attending important external meetings, but said that a dress code which helped keep staff cool, while maintaining a corporate image should be agreed on.

"Employers have got to remember that it's no fun working in a baking office or factory and they should be doing all they can to take the temperatures down," Barber said.