Rail passengers have complained of “roasting” hot temperatures as a new heating and air conditioning system appears to have malfunctioned.

Commuters using the new Thameslink Class 700 trains have complained about uncomfortable chairs with reduced padding, introduced because of new health and safety guidelines.

Now they claim they face temperatures of up to 29 degrees celsius on their journeys. Angered commuters have started an online campaign after facing what they say is months of overheated Thameslink trains.

Some have taken to bringing thermometers on their journeys, and have told the Sunday Telegraph that temperatures between 24 and 29 degrees have been recorded.

Graham Palmer, Head of Research of the South East Rail Group, told the Sunday Telegraph he estimates between 65 and 70 per cent of services are affected.