Unions have stepped up their opposition to driverless Tube trains after a quick-witted driver spotted a young child had fallen between a carriage and the platform.
The drivers' union Aslef said the driver of a London Underground train noticed a tiny hand reaching up from the track when he made a final visual check ensuring the five-year-old boy escaped without injury after the incident on the network's Jubilee Line on Sunday evening.
Aslef said all the automatic devices in place showed the platform was clear and it was safe for the Tube train to depart, adding that the driver's action saved the child from death or injury, the Press Association reported.
General secretary Mick Whelan said: "The driver, on a final visual safety check, saw a tiny hand reaching up from the track. The train remained in position and a young life was saved.
"Mayor Boris Johnson has been playing politics with the issue of driverless trains. He thinks he is currying favour with voters with this stand. How many votes are a young child's life worth? How would he explain to those watching horrified parents that his proposal is a good one?
"On Sunday all the automatic devices showed the platform was clear. Only a driver could have averted a potential tragedy.
"Boris Johnson is wrong to continue to push his policy for driverless Tube trains when it can threaten the lives of London's travelling public. I want him to accept that it is a mistake."
London Underground's network services director Nigel Holness said: "In this case our staff followed their established safety procedures to bring the incident to a safe conclusion and without injury. The whole design and operation of the network would be different with driverless trains and therefore we cannot compare the two.
"Many incidents on the network are, and will always be, customer-related and we will of course always provide fully for handling those safely and efficiently."
Transport for London (TfL) confirmed that the child fell between a stationary train and the platform at Finchley Road station, adding that staff followed their established procedures to "swiftly" respond and bring the incident to a safe conclusion.
The child and parents were able to continue their journeys without reported injury.
It is standard safety practice for drivers at the station to check CCTV in their cabs before moving their trains off from the platforms and this process was followed correctly, said TfL.
Bob Crow, leader of the Rail, Maritime and Transport (RMT) union, said: "The lethal reality of Boris Johnson's driverless trains plan is exposed in this one incident.
"From 7/7 through to a child rescued from the tracks by a vigilant driver, Londoners need to understand the truth that you cannot play politics when lives and safety are at stake every minute of the working day."