Three Appeal Court judges this week ruled that a proposed new kiosk emblazoned with a large, illuminated, digital advertising panel could not be viewed as permitted development.
The council pointed out that the advent of mobile phones has rendered its area's 1,800 telephone kiosks largely redundant and prey to vandalism.
It claimed that the inclusion of a moving-image advertising panel on the back of the kiosk "betrayed the true purpose" of the proposed structure.
But would-be developer, New World Payphones Limited, insisted that its proposed kiosk in Marylebone Road would have state-of-the-art facilities helpful to the public.
Callers would be able to pay by credit card, contactless or cash and have the use of Wi-Fi and a 24-inch display providing an interactive wayfinding capability.
The court heard applications for replacement telephone call boxes and attached advertising screens had "burgeoned over the last few years".
New World sought prior approval for the kiosk - which would replace two old ones - on the basis that it was a permitted development under the Town and Country Planning Act (General Permitted Development) (England) Order 2015 (the GPDO).
The GPDO was changed earlier this year, removing telephone kiosks as a class of permitted development.
However, prior to that, kiosks and other telecommunications equipment could be installed without the need to obtain full planning permission.
Refusing New World's application in 2017, the council said the proposed new kiosk would "add street clutter" and harm the area's appearance.
The company's appeal against that decision was in June last year upheld by a planning inspector, who said the kiosk "would not have an unacceptable effect on the character and appearance of the area".
However, the inspector's decision was later overturned by planning judge, Sir Duncan Ouseley, who said the application was for "a single-dual purpose development", part of which fell outside the GPDO.
Dismissing New World's challenge to that ruling earlier this week, Lord Justice Hickinbottom, emphasised that "mixed use developments cannot take advantage" of the GPDO.
The judge, sitting with Lord Justice Lewison and Lady Justice Asplin, accepted that New World's "subjective purpose" in making the application was irrelevant to the issue of whether the development was permitted under the GPDO.
However, whilst the proposed kiosk itself was then permitted development under the GPDO, the electronic advertising panel "was not within any permitted class".
The judge concluded: "The GPDO could not be used to obtain planning permission for a mixed planning use or 'dual purpose', because to allow it to be so used would allow permission to be obtained for development that was outside the scope of that permitted by the executive, and ultimately by Parliament, under the GPDO, which would be an abuse of the GPDO."
Sir Duncan was therefore "right to conclude that the proposed development fell outside the scope of the GPDO" and that the prior approval granted by the inspector should be quashed on that ground.
New World Payphones Limited v Westminster City Council & Anr. Case Number: C1/2019/0430