Recent headlines offer a flavour of what it can be like to travel on the capital’s underground railway system during a heatwave – “Commuters say London Underground is ‘too hot for humans’”; “Tube lines delayed by heat as Transport for London (TfL) advises only essential travel”; “London’s scorching tube raises alarm over Europe’s brutal heat”; “London’s hottest tube lines feel like fiery pits of hell”.

London Mayor Sadiq Khan has claimed that expanding the ultra-low emission zone (ULEZ) is crucial in a bid to limit temperatures for passengers on the London Underground, as climate change will render trains “unusable for one month in the year by the 2030s”.

TfL, meanwhile, has monitored average monthly temperatures on the tube network and claims to be  investing millions as part of a long-term programme to ensure it can introduce new trains to meet growing customer numbers while also providing more comfortable journeys.

During last year’s heatwave in July, parts of the Underground network reached temperatures in the mid 30s, leaving many sweaty and gasping for water. The Central line was recorded at 36 deg C with the Bakerloo line slightly cooler at 31 deg C and the Circle line the coolest measured at 28 deg C. Meanwhile the PA news agency recorded temperatures of 35 deg C on a platform at Oxford Circus station, and 33 deg C in Edgware Road tube station.

A major trial on London’s Underground system is evaluating the viability of reducing temperatures on the deep tube network. TfL is testing a new cooling system designed to reduce temperatures for tube passengers on hot days.

If the trial is successful and funding is secured, it will be extended to five deep stations on the Piccadilly line – Green Park, Holborn, Knightsbridge, Leicester Square and Piccadilly Circus. Longer term, it could be rolled out across the Bakerloo, Central, Jubilee, Northern, Piccadilly, Victoria, and Waterloo & City lines.

According to TfL: “The Piccadilly line was chosen for this trial as when new, air-conditioned trains with walk-through carriages are introduced to the line from 2025, the current fleet will be gradually withdrawn from service and the frequency of trains in peak hours will rise from 24 to 27 trains per hour from mid-2027.”

The cooling panels work by circulating cold water around pipework within a curved metal structure, while a large fan circulates air through gaps in the panels. The system is being tested by workers at a disused platform at Holborn station and the next stage will see it being used on passengers at Knightsbridge.

Engineers monitoring the prototypes in lab conditions saw temperatures drop by 10 to 15 deg C.

Mr Khan recently told the My London website: “All the new trains we’re ordering now are air conditioned; whether that’s the Elizabeth line, the new Piccadilly line trains, or the four [tube] line modernisations taking place.

“Some of our trains are older – 30, 40 years old – which aren’t air conditioned, and on some days in summer they can be intolerable. And, so we’re lobbying the government for capital support to try and upgrade those trains as soon as we can.”

London Underground is one of LH-plc’s largest customers with the company servicing and repairing the air conditioning inside the trains, mainly the drivers’ cabs. LH-plc’s cutting-edge railway air conditioning refurbishment and servicing centre in Wimbledon, south-west London combines state-of-the-art facilities with well-qualified and experienced engineers to offer an exceptional service that is both reliable and offers premier quality.

The company – which carries out work on behalf of many of the major UK rail carriers as well as the London Underground tube operators – employs a highly skilled team of specialist engineers boasting more than 30 years’ experience in this specialist sector, having developed extensive knowledge and unique engineering skills focused on the requirements of railway air conditioning systems.