A major capital city that welcomes very few British tourists is spending £4bn on a huge upgrade to its Metro railway system.

Iran’s capital, Tehran, is – with more than 9 million residents – the second most populous city in the Middle East after Cairo.

However, ongoing tensions with the West mean this ancient city – which dates back some 6,000 years – doesn’t get many visitors.

But this hasn’t stopped the Islamic Republic of Iran – which is regularly accused of sponsoring terrorism – of spending billions on improving its transport infrastructure. Once finished, the Tehran Metro will be bigger than those in London and New York – which are two of the world’s biggest, outside of China or Moscow.

The Tehran Urban & Suburban Railway is already the largest metro system in the Middle East and carries more than 3 million passengers every day.

Tickets cost 5,300 Iranian Toman, less than 4p – and pre-booked tickets are even cheaper. Despite these cheap fares, by 2040 four new Metro lines will be added to the seven that already exist – with extensions also being built.

Three of these new lines are already being built – as are extensions to lines 2, 4, 6 and 7. Line 8 is a planned circular line with 34 stations – 21 of these will be new constructions.

Line 9 is another circular line, with 39 stations. It will boast 27 newly-built stations. Line 10 – with 35 stations – will run along a west-east corridor from Vardavard Metro Station in the west of Tehran towards the area of Kosar aqueduct in the east, with an interchange to the extended line 4.

Line 10 will be serviced by 35 stations. It will run along a west-east corridor from Vardavard Metro Station in the west of Tehran towards the area of Kosar aqueduct in the east, with an interchange to the extended line 4.

The £4bn project will involve new tunnels, high and low-pressure energy systems and workshops. New safety systems, control facilities, signalling systems, and switching and communications systems are also being installed.

An automatic fare collection system is also being created. Excavation work for metro line 10 began in August 2023.

All three of the new lines are scheduled to be completed by the start of 2029. Once all 11 lines are finished in 2040, the Tehran Metro will have a total length of 430 kilometers.

This would make it the biggest Metro system outside of China or Russia. London Underground currently holds that title, but its total length is only 402 km.