Metropolitan Line Extension ('MLX'), formerly the 'Croxley Rail Link'

Three Rivers District Council supports the concept of a Metropolitan Line Extension (formerly the Croxley Rail Link), a proposed extension of the London Underground Metropolitan line, from Croxley Station to Watford Junction. The scheme was promoted by London Underground in partnership with Hertfordshire County Council and Network Rail but is not currently being taken forward (see the end of this page for updates).

Three Rivers District Council and Watford Borough Council were also committed to the delivery of this important project as it would clearly benefit local communities by:

  • Improving access to public transport for local residents (more than 2,500 households would be within 10 minutes walk of the two new stations)
  • Creating better connections between Watford and Croxley Green, with new routes to Watford General Hospital, Croxley Green Business Park and other Industrial Estates, which would increase access to employment opportunities for local people
  • Providing access for Metropolitan line passengers to West Coast mainline National Rail links from Watford Junction station

This scheme would involve a significant level of construction work. A more detailed works programme is currently being compiled by the project team and was published once detailed engineering designs are completed. 

London Underground supported the scheme because: "the Metropolitan Line Extension would greatly enhance the rail network for those living, working and visiting the area. It would support growth and regeneration in the Watford area by creating new links to Watford General Hospital and the new health campus, Croxley Business Park and Cardiff Road Industrial Estate.

Two new stations would be created at Cassiobridge and Watford Vicarage Road, served by new walk-through air-conditioned trains every ten minutes to and from central London during peak hours. The existing Watford Metropolitan station would close to the public following the opening of the new stations, but was retained for operational purposes.

Enabling work, including ecological and environmental protection work, is already being undertaken for the project. It is anticipated that construction of the extension could commence from 2016, with a target to complete the transformative link in late 2020". 

If you have any questions about the scheme, please refer to London Underground using the following contact details: 

Phone: 0343 222 2424 (24 hours)
Post: London Underground Community Relations, 5th floor, Palestra, 197 Blackfriars Road London SE1 8NJ

If you are interested in the work that Three Rivers District Council did to support the scheme, please contact Transport & Projects at 01923 776611 or email

Transport for London provided the following update statement on the 25 January 2018:

“We have always been keen to see the Metropolitan Line Extension progress and the Mayor presented the Government with a practical proposal to find a solution to the funding gap and cost risk. We remain open to helping assist the Department for Transport in finding alternative schemes that may be more affordable. 

“We are currently delivering one of the world's largest programmes of transport investment, including building the Elizabeth line and modernising Tube lines and stations. Huge improvements to the frequency and reliability of services are being delivered on more than 40 per cent of the London Underground network, including the Metropolitan line.” 

Further information

  • After taking on the Metropolitan Line Extension from Hertfordshire County Council, TfL undertook a detailed review to establish the true cost of the project.
  • Following this extensive work we estimate that to complete the extension, we would need to more than double the funding commitment we have already made.
  • The most recent estimate (from February 2017) of the final cost of the MLX is £357.8m. This is £73.4m higher than the current funding package, and doesn’t take into account the accountability for cost risk on the project beyond that estimate.