A new Metro- style service with trains as frequent as on the Tube will cover outer London in four years' time.

Dubbed the "London Overground", it will connect 71 stations in 20 boroughs in the first major step to an orbital rail network for the capital.

From November next year, the service will run on the four existing lines that form the North London Railway (NLR).

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It will also cover the new East London Railway (ELR), once the £1 billion East London line extension is completed in 2010.

A new link between Dalston and Highbury & Islington, estimated to cost £50 million, will connect the two networks. This will allow passengers to travel all the way from Richmond in the south-west of the capital via the northern suburbs to West Croydon in the south.

Trains will depart every eight minutes, instead of every half-hour as is currently the case. Run-down stations will also be upgraded and made safe.

The Overground will have its own roundel, similar to that of the Tube, and will be incorporated on the iconic Tube map.

"For decades, national rail services in London have been neglected and in many cases under-utilised," mayor Ken Livingstone said as he unveiled the new scheme at City Hall on Tuesday. "The dawn of 'London Overground' will start the much needed revitalisation of London rail services."

The change was made possible by a government decision in February that Transport for London (TfL) will take over NLR in November next year.

NLR, currently operated by Silverlink, includes:

  • The North London line (Richmond to North Woolwich);
  • West London line (Willesden Junction to Clapham Junction via Kensington Olympia);
  • Euston to Watford Junction; and
  • Gospel Oak to Barking.

The mayor said the new Dalston junction would be ready by 2010, in time for the 2012 Olympics. "By joining together the North and East London Railways, we will create a new rail artery around the city, serving 20 London boroughs."

If a second phase of the East London line extension is approved, the Overground will form a full circle in outer London. The government will decide during its spending review next year whether it will pay for the proposed link between Clapham Junction and Surrey Quays, much of it on existing track.

OVERGROUND TIME SCALE

  • 2007 Stations upgraded on the North London Railways
  • 2009 New north London trains increase service frequency
  • 2010 East London Line extension between Dalston and West Croydom completed
  • 2010 New Dalston link connects east and north London networks
  • c 2016 Overground is full circle (If phase two of East London Line extension, between Surray Quays and Clapham Junction, is approved)

The total bill for the Overground will be around £1.5 billion. Of that, £1.4 billion has already been secured as part of TfL's £10bn investment programme - including £1 billion for the first East London line extension and £400 million for upgrades on NLR.

From next November, NLR stations will be improved with more staff, Oyster ticketing, CCTV and better lighting. More frequent services will only start in 2009, once a new fleet of 24 three-car trains is introduced to the north London network.

Although TfL will manage the Overground lines, a private company will operate the trains. Four firms have been shortlisted for the contract: Govia, MTR Laing, National Express Group and Nedrail. The successful bidder is due to be announced next summer.

But Bob Crow, the secretary of the Rail, Maritime and Transport (RMT) union, said the plans to privatise the East London line were "completely unneccessary".

He added: "After all the painful experience of privateers running the national railways and raking in millions for making a total hash of promised improvements to the Tube's infrastructure, it defies belief that the same mistake is proposed for the East London line."