Employment Rights Bill - high temperatures

The Government has unveiled details of its Employment Rights Bill, which aims to eliminate exploitative practices, such as the use of zero-hours contracts and "fire and rehire" tactics.

Among the proposals, the Government has said it will look at "how to modernize health and safety guidance with reference to extreme temperatures". 

Unions have called for a maximum temperature of 30C indoors or 27C for strenuous work. London has averaged 6 days per year over 30C over the last decade.

I'd like to know what the impact on businesses would be if workers are given the right not to go into work because of hot (or cold) weather.