The answer to the question is technically NO. There is no maximum temperature that a workplace is allowed to be.
However, this is not a clear cut issue. During working hours the temperature in all indoor workplaces must be reasonable and employers must continue to have regard to all Health and Safety at work legislation.
They must also give consideration to the type of work that is being carried out by employees such as physical manual workers, as they may need to be given additional rest breaks which would not necessarily be applicable to office based workers.
Employees should talk with their employers if they are struggling due to the heat and the employer should consider what measures to take to make the working environment more comfortable.
Additional consideration may need to be given to vulnerable workers, such as young or older people and also those who may be pregnant.
Another burning question whether an employer should ‘relax’ any dress code to assist with keeping their employees comfortable.
A dress code is often in place to ensure employees are dressed appropriately. Many employees may need to wear a certain uniform or dress in a certain way to ensure that Health and Safety Legislation is meet such as builders need to wear the appropriate PPE (Personal Protective Equipment) such as hard hats or steel top cap boots and therefore an employer cannot reduce this type of dress code.
To conclude, during the days when the weather is extremely hot both employers and employees must act reasonably.