London Underground tunnels could soon be carrying a super-fast broadband internet service, if plans being worked on by TfL come to fruition.

By laying fibre optic cables in the tube tunnels, combined with some space within the stations for the optical network equipment, TfL plans to build its own broadband network offering a massive 20Tbps capacity (2000 Gbps).

London Underground already carries telecoms networks for external companies, such as Virgin Media, Cable & Wireless and Verizon, in addition to its own signalling and control communications, so the principle of running fibre optic cables in tube tunnels is a well-proven one.

What is being planned is a backbone network that is then used to boost capacity offered by ISPs to consumers and businesses, and would be used to address a number of “not-spots” in London where broadband speeds are slower than expected.

The key advantage of using the tube tunnels is that TfL will be able to roll out a high-speed core network extremely quickly and without digging up roads across the city.

Some of the worst of the not-spots happen to run close to existing tube lines, such as a large cluster of poor internet speeds along the Jubilee line between Bermondsey and West Ham, as well as along the Metropolitan and Bakerloo lines around Wembley.

Once the high-speed broadband cables are laid in the tube tunnels, short digs will be required to local delivery points using higher fibre count cables allowing for additional local connections from cabinets and in building equipment.

One of the other benefits of using tube tunnels to run cables is that they run pretty much in a direct line point-to-point, and by reducing the length of cable, and the network switches in-between, they are able to reduce latency on the service — which makes it particularly desirable to data centres and high-volume trading by financial firms, where milliseconds can give a commercial edge over rivals.

To move forward, TfL is making a bid, supported by the Mayor of London and a group of London councils, for government funding for the scheme.

If successful, the funding, which is being made available by the Department for Digital, Culture, Media and Sport’s Local Full Fibre Networks Challenge, would be used to extend the fibre-optic connectivity on the underground network to public buildings near to tube stations, improve connectivity and end remaining not-spots in central London.

Working with 8 central London Boroughs and OPDC will also ensure that the investment is targeted in a way that maximises the availability and benefit of gigabit capable broadband services to public sector, SME and residential users.

If the funding application is successful, work to start installing fibre could begin later this year, with residents and businesses benefiting from faster broadband from 2019.

The use of old tunnels under London to improve its communications is not entirely new.

Thames Water allows its sewers to be used by Geo Networks to carry broadband cables. In the 1980s Cable and Wireless bought up an old network of hydraulic power pipes under the City of London and laid its fibre optic cables through that.

More famously, London Underground was used during WW2 to carry telephone cables for the government.

Telephone lines from Whitehall were routed via the Bakerloo line to Waterloo, then up to the City of London via the Waterloo & City line. The government also used the tube tunnels to run phone lines out to the countryside, taking advantage of the deep tunnels to protect their phone lines from being damaged by bombing raids.

At the time, a bundle of cables could carry a handful of phone calls, but the network being planned by London Underground today could deliver millions of lolcats across the city every second.