Overheated: Jubilee Line tops London Tube temperature table

On the hottest afternoon of the year, London’s warmest Tube line was the Jubilee – with temperatures in trains on the stretch between Bond Street and Baker Street reaching 33.4C, which corresponds to 92F.

The reading is significantly above both the shade temperature in London and the 30C maximum stipulated by the European Union for transport cattle, sheep, pigs over long distances. 

The Independent conducted a survey of seven underground lines in Zone 1 of the capital. Every temperature taken inside a train exceeded 30C. 

In joint second place were the Piccadilly and Bakerloo lines, both at 32.8C.

Services on the Bakerloo Line were disrupted by “heat-related temporary speed restrictions” on the overground section northwest of the city centre.

London has the oldest Underground railway network in the world, with the deep-level Tubes operating through narrow tunnels with limited opportunities for ventilation. 

About half of the surplus heat generated by the trains occurs when they brake. The friction generated by moving through air also increases the temperature.

The Central Line, which in a 2018 survey was found to be warmest, took fourth place; between Tottenham Court Road and Oxford Circus, the temperature was 32C.

Fifth-hottest was the Northern Line, at 31.7C. The Victoria Line was the coolest of the deep Tube lines, at 31C.

The world’s oldest stretch of underground line, from Farringdon across to Paddington, is a sub-surface line with larger tunnels and better ventilation. 

The temperature reading between Farringdon and King’s Cross was 30.4C.

Passengers on the new generation of Routemaster buses, which were initially supposed to operate with open rear doors, are experiencing temperatures almost as high as the warmest Tube line.

A reading of 33.1C was taken on the top deck of route 24 along Charing Cross Road.

Other rail lines around the UK experienced problems, with passengers using GWR services to and from London Paddington facing long delays and widespread cancellations.

Signalling and points failures were among the causes.

With tens of thousands of passengers finding their journeys taking hours longer than normal, the train operator tweeted: “There are several delays across the network due to multiple reasons at present, as we recover normal service.

“We are doing all we can to ensure services resume to normal.”