A quarter of London councils have removed pay and display parking machines in favour of smartphone-based apps, figures show.
Eight boroughs across the capital have replaced all their machines with cashless alternatives.
Bromley and Enfield both stopped using traditional pay and display machines in April. Harrow, Westminster and Kensington and Chelsea have axed all their machines too.
The reason for the shift is mobile phone providers are switching off 3G data networks, which run the parking meters.
Campaigners have warned that the expansion of cashless threatens to isolate disabled or elderly people.
Bromley said it would cost £1million to update all its machines. Therefore, motorists in the borough can no longer use cash to pay for parking and are encouraged to download the RingGo app or call or text to pay.
Anyone without a mobile can call and pay in advance from a landline but this does not guarantee them a space.
Cameras clock cars entering and leaving an app-based car park and cross-check with payments received.
At least half of all London councils – 16 out of 32 – have axed some or all of their machines.
One benefit of using a smartphone app is that it often gives users the ability to add extra time to their stay without having to return to their vehicle.
But there are numerous providers, such as RingGo, JustPark, PAYBYPHONE and Parkopedia, and they usually require users to key in their contact information as well as car details before they can use their app.
As with any online programme, there is also a real risk of scammers.
Caroline Abrahams, charity director at Age UK, warned that the measures could exclude old people.
She told the BBC: “If you are an older person who is reliant on your car for getting around but you have no means of legally parking it near to where you want to go then you may be left feeling there is little point going there at all, and that would be very sad for anyone affected, and very bad news for businesses too.”
A Department for Levelling Up, Housing and Communities spokeswoman said: “Councils should determine what is best for their own area and have a duty to ensure that they do not discriminate in their decision-making against older people or those with vulnerabilities.”
A spokesperson for the Local Government Association, which represents councils in England and Wales, said: “The removal of the 3G network is posing considerable challenges to some councils who operate physical parking meters.
“This change, along with other customer trends, has led to councils digitising parts of their parking services.”
