Boris Johnson opens new rail link on London Overground

The Mayor of London, Boris Johnson, has opened a new rail link on the London Overground that he hopes will eventually lead to a "M25 of the railways".

The new £50m line connects Dalston Junction to Highbury & Islington and completes another section of the outer London rail orbital.

The final link from Clapham Junction to Surrey Quays will be finished by the end of 2012.

BBC London's transport correspondent Tom Edwards reports.