It's no good hoping for fog - you're up against the mother of all snoops

No one is to escape the congestion charge. Not even the congestion charge patrol vehicles. That was the unintended message from Transport for London as it gave The Independent on Sunday an exclusive preview of its mobile tracker units last week.

From early tomorrow morning, commuters will find 10 white Mercedes vans ranging around town. With twin cameras sprouting from their roofs, they will not be hard to spot. And when the clock strikes 7am they will begin the job of sweeping up all rogue vehicles that have dodged into the central area and somehow missed the fixed cameras at the entrances to the zone.

The vans are fuelled by liquid petroleum gas and so, in theory, exempted from the £5 daily congestion charge. But in practice it is the wrong sort of gas. "So for the time being we're having to pay," admitted TfL.

Everything else about the vans seems to be working. There is disappointingly little gadgetry inside, just a couple of computer screens, one displaying a moving collage of number plates as they are captured by the cameras; not much is going escape their surveillance even on a busy main road, as the system generates 25 frames a second and the pictures are undeniably clear.

The same technology is already used by City of London police in the "ring of steel" set up protect the capital's financial heart from terrorism. The cameras take infra-red and colour pictures which means that they can see your number plate even when you cannot see them – in thick fog for example.

But vehicles and their registration plates are the only things to be filmed. TfL insists pedestrians should have no concerns about any unwarranted spying.

There is no drama, no blinding flash when cars go by. The van's equipment quietly absorbs the images, munching its way through plate after plate as the traffic roars through.

TfL's head of visual imaging, "Matthew" – not his real name because TfL is nervous about the threats made to its staff since the charging scheme was announced – claims most opponents of the fee are deluding themselves when they claim the cameras can be beaten. He logs on to the "Sod U Ken" website every morning so that he can read about the latest scams – and have a good laugh.

Tomorrow, as the vans start work, their doors will be firmly locked against any possible threats. TfL is also keeping secret the 300 city centre sites where the mobile enforcement teams will park and snoop (though apparently they are all close to food and lavatories, and staff will have to put cash in the parking meters, just like everyone else).