A five-year-old boy had a lucky escape after falling between a London Underground train and the platform at Finchley Road station in north London.

Drivers’ union Aslef said the driver of the Jubilee line Tube train saved the boy from death or serious injury after spotting a tiny hand reaching up from the track during a final visual check before the train pulled away.

Aslef said the incident on Sunday evening reinforced its opposition to driverless trains on the Tube network.

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 the child fell between a stationary train and the platform, adding that staff followed 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.