Electric black cabs zooming through the streets of London are still at least several weeks away after a setback in its payment system.

The meters installed are having trouble keeping track of fares and are not charging at the same rate as diesel cabs. In the test models, fares are lower because the system is not pulsing - recording distance and time - as well as diesel models. The cars are not yet available for customers on London streets and the results have only been discovered during internal tests.

The glitch is made all the more complicated by a ruling that stipulates all new black cabs has to be electric. Hundreds of taxis have been ordered and will join about 23,000 diesel-powered cabs already in operation.

According to The Guardian, Transport for London and LEVC were working together to fix the issue. "The signal from the vehicles and the meters are not lining up and we are working on a solution to fix that issue. We're working to get an appropriate converter to get the vehicles license by (Transport for London) and over to customers."

In a statement sent to IB Times UK, LEVC said a solution has been found. "Deliveries have been put on hold as a result of an unexpected issue with compatibility with the taxi meters and the taxi," a spokesperson said. "The problem is understood, and it involves the pulse messages sent between the vehicle and the meter."

"We have a solution and are working with TFL and the third-party meter suppliers to get the updated, approved meters installed so we can begin customer deliveries in earnest."

The cost of the new TX electric cab is also proving to be a stumbling block for early adoption. It will cost black cab drivers £12,000 more to buy the TX compared to a diesel model. Drivers can lease one for £177 a week over five years, or face an outright cost of about £56,000 (subsidised by a £7,500 grant).

Licensed Taxi Drivers' Association general secretary Steve McNamara praised the TX as a step forward but questioned its high price. "It is state-of-the-art," McNamara told The Guardian. "We'd have gone from a 1950s Ford Anglia to a Tesla overnight with this. And we could be leading the charge in persuading the rest of London to be electric, clean and green.

"At the moment people are very hesitant. We've got to pay £12,000 more for a vehicle that we don't know the reliability or durability of, at a time when the market is being squeezed by that company (Uber)."

McNamara also feared there was not enough rapid charging stations in London. The TX has a range of about 70 miles but a backup petrol engine can stretch it to 377 miles.