The Met Office issued its first ‘red extreme heat warning’ for parts of England for Monday and Tuesday. This warning means the level of heat can have adverse health effects.

People have been urged to change their routines and minimise exposure to the sun and heat. But for many workers, they will have to bear the scorching temperatures.

The Trades Union Congress (TUC) called on bosses to make sure that any staff working outdoors such as builders, postal workers and street cleaners are protected from the sun and heat. It also wants to see employers forced to take action when indoor temperatures exceed 24°C.

But for those who are outside for lengthy periods of time, they are at risk of sunstroke, heatstroke and even cancer, the TUC warned.

And working in hot weather can also lead to dehydration, tiredness, muscle cramps, rashes, fainting, and in the most extreme cases, loss of consciousness.

It urged bosses to allow workers to avoid tasks between 11am and 3pm when the risks are most acute. Outdoor workers should also be given sunscreen, plenty of breaks should be provided, as well as drinking water. On the issue of uniforms or dress codes, these should be relaxed, it said.

For those who drive for a living, the TUC said bosses should provide cars, cabs, vans and lorries which have air conditioning. As such, it is calling for vehicles without air con to be temporarily taken out of use during the heatwave.

However, there is no legal obligation for work vehicles to be installed with air conditioning or for employers to provide sunscreen to protect employees, though the TUC argues this should be considered as PPE (personal protective equipment) for outdoor roles.

But, there is a legal requirement for workplaces to be safe and temperatures ‘reasonable’. Under Section 44 of the Employment Rights Act 1996, workers have the right to withdraw from, and refuse to return to, a workplace that is unsafe.

Workers are entitled to remain away from the workplace if, in their opinion, the prevailing circumstances represent a real risk of serious or imminent danger which they could not be expected to avert.

The TUC explained this law protects a worker from detriment – including loss of pay – if they leave the workplace due to a serious or imminent danger.

If an employer refuses to pay someone who left work in order to protect their or other workers’ safety, “they should expect a legal challenge”, the TUC said.

However, the TUC advises people to speak to their union first before using their rights under Section 44 of the Employment Rights Act. But it confirms that workers don’t need to go through a union to use this right. Workers can simply inform their boss of their intention.

TUC general secretary, Frances O’Grady, said: “This week we will see temperatures soar. Without adequate protection outdoor workers could be in danger.

“Bosses must ensure their staff are protected with regular breaks, lots of fluids, plenty of sunscreen and the right protective clothing for those working outdoors – or relaxed dress codes for those working in shops and offices.

“Anyone worried about their working conditions should join a union, it’s the best way to stay safe at work and make sure your voice is heard.”