PRIME Minister Andy Burnham rejected calls to set a maximum workplace temperature by a coalition of unions and climate activists today, as the Met Office predicted this summer will become Britain’s warmest on record.The Heat Strike campaign called on Labour to set a national maximum indoor working temperature of 30°C, dropping to 27°C for those doing strenuous work.Coalition campaigner Liam Geary Baulch said: “Everyone is feeling the effects of the climate. The government must protect workers when it’s too hot to work and safeguard everyone’s future.