The Mayor's Office has confirmed Boris Johnson authorised the highly-controversial purchase of water cannon - despite not yet getting the go-ahead from the Home Secretary.
City Hall says buying the German vehicles now will mean savings of £2.3million compared to buying new water cannon and ensures they are ready as soon as possible'.
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Official readings are recorded three metres in the air but a study found levels of nitrogen dioxide (NO2) were higher at pushchair level.
Tubes, trains, trams, buses, cable cars, river buses, taxis and going by foot - your guide to getting around during the strike.
Union officials rejected a revised offer from Underground managers during a meeting at the conciliation service ACAS this afternoon.