They are among the most iconic symbols of London and a design classic, yet technology has rendered them almost obsolete.

But now the classic red telephone box has been handed a lifeline.

A charity has unveiled plans to convert a central London kiosk into a mobile phone charging station.

A planning application for alterations to the box on Brompton Road, Knightsbridge, has been lodged with Kensington and Chelsea Council. If the scheme proves popular, it could be replicated around the capital.

‘The K2 and K6 red phone boxes are iconic pieces of both engineering and architecture,’ explained Miles Broe, principal architect at Miles Broe Architects, who drew up the plans. ‘The aim of this proposal is to redefine their usage to suit modern day needs and requirements without compromising their external appearance.’

Inside, however the original phone, handset and cash box will be stripped out, the box thoroughly cleaned and repainted, and chargers installed so that passers-by can plug in their phones.

The service will, initially at least, be free.

‘The concept of a public telephone box is now outdated,’ added Mr Broe. ‘The proposed new use maintains their iconic appearance but re-invents their use to suit the 21st century.’

The project is the brainchild of Thinking Outside the Box, a charitable trust which helps provide jobs and training for homeless people. It has already kitted out phone boxes as miniature coffee shops and sweet shops staffed by homeless workers. Others have been fitted with life-saving defibrillators.

The K Series phone boxes were first launched in 1936.

Earlier this year they were voted the greatest-ever British design, beating out the black cab and the Routemaster bus.