The Met Office has forecast that the mercury will reach highs of up to 27C in the UK today and its only going to be slightly cooler on Friday.
Very high levels of pollen and UV mean that hay fever sufferers are in for a difficult time.
Met Office forecaster Mark Foster said it is possible the hottest day for the year for all parts of the UK could be bettered this week.
But how high does the temperature need to go before it becomes too hot to work?
Workers must be protected from the heat
The TUC has called on bosses to make sure staff working outdoors are protected from the sun and the heat.
Workers including builders, agricultural workers and gardeners who are outside for lengthy periods in high temperatures are at risk of sunstroke, sunburn and skin cancer, the union organisation warned.
TUC general secretary Frances O’Grady said: ‘We all love to see the sunshine, but working outdoors in sweltering conditions can be unbearable and dangerous.
‘Bosses must ensure their staff are protected with regular breaks, lots of fluids, plenty of sunscreen and the right protective clothing.’
Unfortunately, there isn’t a legally defined maximum temperature for the workplace but the Heath and Safety Executive has issued a number of guidelines.
They have said that, during working hours, the temperature in all indoor workplaces must be reasonable.
The temperature should be at 13C if employees are doing physical work but there is no maximum temperature given due to high temperatures of working in some places, for example a glass works or foundry.
While ‘reasonable’ is rather ambiguous, the law does say that an employer must act if a ‘significant number of employees are complaining about thermal discomfort’.
If this is the case then your employer should carry out a risk assessment.
There are six basic factors an employee should look at including air temperature, radiant temperature (ie, the temperature radiating from warm objects), air velocity, humidity, and what clothing or insulation workers are expected to wear.
A HSE spokesperson said: ‘As an employer you should be aware of these risks and make sure the underlying reasons for these unsafe behaviours are understood and actively discouraged and/or prevented.
‘The more physical work we do, the more heat we produce. The more heat we produce, the more heat needs to be lost so we don’t overheat. The impact of metabolic rate on thermal comfort is critical.”