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Every year, more than 9,000 Londoners die prematurely from long-term exposure to air pollution. Many live in areas where air pollution exceeds safe legal levels — mayor Sadiq Khan has described it as “nothing less than a serious public health crisis”.

Exposure causes lung and heart disease, and is linked to diabetes, asthma, cancer and obesity — health problems resulting from exposure to air pollution cost us more than £20 billion a year.

Mr Khan wants to make London the greenest global city, with 80 per cent of trips in 2041 being made on foot, bike or public transport. “TfL is one of the best strategic transport planning authorities in the world, with lower levels of car ownership in London and modal share of journeys [by transport other than car] higher than anywhere else in the UK,” notes Leo Murray, director of climate action charity Possible.

“But within the city limits, transport is the biggest emitter of carbon dioxide by a massive margin.”

In 2018-19, TfL produced 1.75 million tonnes of carbon dioxide emissions, compared with 1.94 million tonnes in 2017-18. Emissions of particulate matter also reduced by 12 per cent to 60 tonnes. These figures include emissions from black cabs and private hire taxis.

London Underground has been electrified since the 1960s but more energy-efficient trains are being introduced and technologies such as regenerative braking will reduce the amount of energy required. TfL, one of London’s largest users of grid electricity, is also developing plans to purchase electricity from renewable sources.

But air quality is still a massive issue on the Tube, partly because the “fresh” air drawn in via surface ventilation shafts is so polluted. In November 2019, scientists at King’s College London found that concentrations of fine particles in air on the Underground network were approximately 15 times greater than concentrations on the roadside in central London. The particles included heavy metals from rail and brake wear.

Murray explains: “By far the worst line is the Victoria line because it’s so deep underground and entirely enclosed, so polluted air is never pushed out into the open. It just accumulates.”

London already has one of the largest and greenest bus fleets in the world with routes 43, 134 and 94 among the latest to introduce electric buses, and more than 85 per cent of the capital’s 9,300 buses meeting the ultra-clean Euro VI standard.

More than 3,000 taxis in London are “zero emissions capable” (electric or hybrid) and 25 per cent of the UK’s electric vehicle charge points are in the capital.

Launched in 2019, prior to suspension due to the coronavirus, the world’s first ultra low emission zone (Ulez) has resulted in 13,500 fewer polluting cars being driven daily into central London. It has reduced nitrogen dioxide and carbon dioxide emissions from road transport by 31 per cent and four per cent.

Giulio Ferrini, head of built environment at Sustrans in London, would like Ulez to be extended as far as the M25, and use a smart charging model. Once “rat-run” traffic has been diverted away from residential streets, in “low traffic neighbourhoods”, driving becomes less convenient. Inspired by filtered traffic systems in Dutch cities Amsterdam and Utrecht, low traffic “superblocks” are being pioneered in Barcelona.

In Waltham Forest’s mini-Holland, this resulted in traffic levels falling by more than half inside the residential area and by 16 per cent including main roads.