This is a trip on the Docklands Light Railway in London, or the DLR as it is known. It's a seven minute journey from Mudchute station to Heron Quays (although for some unknown reason I say Heron Gate in the recording. Heron Quays is correct). From the Transport For London website:

'The Docklands Light Railway is an automated light metro system primarily serving the redeveloped Docklands area of London and providing a direct connection between London's two major financial districts, Canary Wharf and the City of London.'