The union has joined the TUC in calling for a legal limit on how hot it can be in a workplace as forecasters predict a record high of 41 degrees celsius in England and the Met Office issues a red warning for heat – covering cities including London, Manchester and York – for Monday and Tuesday.
The GMB wants to see a maximum workplace temperature of 25C enshrined in law, while the TUC wants there to be a requirement to stop work if indoor temperatures reach 30C, or 27C for those doing strenuous jobs.