The ‘West London Orbital’ would run from West Hampstead and Hendon towards Hounslow, making it the seventh Overground line on the Transport for London (TfL) network.
But according to London Mayor Sadiq Khan, government funding will be needed to fully realise the project.
Last year, he said that he would be lobbying the Government for this in advance of the spending review expected this spring.
Meanwhile, Hounslow Council has approved more cash to fund preparations for a formal bid for the line’s construction.
The local authority’s cabinet last week approved £714,000 worth of investment in the project.
Its final route is yet to be revealed, but initial proposals would see trains stop at 15 stations, including Cricklewood, Neasden, Harlesden, Acton, Brentford and Isleworth.
In some instances, existing platforms will be used but new stations would be needed at Neasden, Harlesden, Old Oak Common and Lionel Road.
Trains would make use of existing tracks that are currently used for freight services.
On current timescales, an application to secure approval to build the new Overground line would not be made until the late 2020s.
