Our reporter Sangeeta Kandola went to meet Chris Brittain and Beau Brown in September last year - best friends, both have cerebral palsy.
Beau, from Weybridge, recently received an operation in American to help him walk. Chris meanwhile, from New Haw in Surrey, is still waiting for enough money to be raised to pay for a similar operation.
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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.