A network of express buses that connect London’s suburbs was unveiled on Tuesday by Sadiq Khan.

The “Superloop” will draw together existing services, such as the X140 and X26 that serve Heathrow, with proposed new orbital routes linking town centres such as Harrow and North Finchley, and North Finchley with Walthamstow.

It is part of a £6m investment by the Mayor in outer London bus services alongside the expansion of the ultra-low emission zone to the Greater London boundary.

Few of the new services will be in place by the time the Ulez is due to expand on August 29. But the vision set out on Tuesday is for a network of limited-stop buses offering speedier connections between major suburban hubs.

Mr Khan said: “When I made the tough decision to expand the Ulez London-wide, one of my key commitments to Londoners was to improve transport links in outer London.

“Today I am delivering on that commitment as we announce the Superloop, the game-changing new network of express buses that will add over four million additional kilometres to our bus network in outer London, linking stations, town centres, hospitals and transport hubs.

“These new routes will make it much easier for Londoners to get around the capital, and help build a better, greener London for everyone.”

The wheels on the bus: Superloop’s indicative map

The Superloop will include the X140, which connects Heathrow and Harrow, and a more frequent route X26, which runs between the airport and West Croydon.

Later this year the frequency of the X26 will be doubled to a bus every 15 minutes, rather than two an hour at present.

In the coming months, Transport for London will consult on a new express route linking Harrow and North Finchley.

Following that, views will be sought on future sections of the Superloop. These are likely to include a section between North Finchley and Walthamstow and between Walthamstow and the Royal Docks via Ilford. Links are also proposed between Bexleyheath, Bromley and Croydon.

One of the buses that will travel around the Superloop

The Superloop is also likely to incorporate the existing “limited stop” east-west route 607, between Uxbridge and White City, and the north-south X68, which links Croydon and Russell Square.

The “illustrative” map produced by TfL also indicates that the proposed X239 outer to inner London service, which would link Grove Park and Canary Wharf via the Silverwall tunnel, with no stops between the Sun in the Sands roundabout and Leamouth on the north side of the Thames, would become part of the network.

The X239 is proposed to run every eight minutes on weekdays but not start until 2025, when the Silvertown tunnel is due to open.

The Superloop buses will feature “retro” liveries and a new roundel to help passengers identify the express routes. The new branding will also feature on maps and timetables.

TfL data shows that the X140, the newest express route, delivered a 10-15 per cent increase in weekday demand. Customer satisfaction increased and nearly four in five said they would use it more often.

Fares for the Superloop will be the same as “normal” buses - £1.75 – with the Hopper fare also in operation. This allows passengers to switch buses for no extra cost within an hour of starting their journey.

This opens up the possibility of using express buses for part of a journey and then switching to a regular bus. The X140’s 13 stops in each direction interchange with 42 other bus routes and seven rail lines.

Alex Williams, chief customer and strategy officer at TfL, said: “The Superloop is the jewel in the crown in our plans to strengthen alternatives to the private car ahead of the Ulez expanding London-wide.

“For the first time we will be bringing a number of the capital’s town centres together with express orbital routes. We know these kinds of services are hugely popular from what we have seen in the rise in the number of people using the X140 during the week.”

But Nick Rogers, the City Hall Conservatives transport spokesman, said: “Sadiq Khan’s Superloop announcement is a Superflop, amounting to nothing more than a repackaging of existing routes and vague promises that will not be delivered before his Ulez expansion hits Londoners.

“This is a microscopic level of investment. The mayor’s rushed plans have been thrown together in a panic, and do nothing to address the devastating impact of his Ulez tax.”

Mr Khan has already pledged to provide an additional one million kilometres of extra bus services in outer London, though this adds less than one per cent to the total mileage of the capital’s 700 routes.

John Holland-Kaye, chief executive of Heathrow Airport said: “Bus routes are vital for thousands of colleagues and passengers travelling to Heathrow. We welcome the announcement of a Superloop service.”