Behind the scenes at the bleak Black Country pound where untaxed cars are crushed

But most of the attention is focused on the black Audi S5 coupe. It might be four years old and a bit grubby, but a wash and a valet should see it fetch £35,000.

But we're not on a car dealer's forecourt or outside an auction house, and the cars parked up are not here with their owners' consent.

This large, bleak expanse of land, tucked behind a nondescript road in the heart of the industrial Black Country, is where your car is liable to end up if you don't pay your car tax.

As we speak, a new arrival comes in. A blue Vauxhall Astra is lowered lifted by crane from the back of the truck, and left to fester with all the other seized cars until either its owner reclaims it, or – more likely – it gets sent to the crusher.

A few streets away Jo Halfpenny has been alerted to another target. The gleaming white BMW already stands out from the other vehicles in the road, and the big yellow wheel clamp and windscreen sticker that the DVLA enforcement officer places on it only draws more attention. If the tax is not paid within 24 hours, it too will be taken to the pound.

Why would anyone risk losing a car, which again is probably worth about £30-40,000, for the sake of a few hundred quid in car tax?

"Sometimes, if the vehicles have been involved in criminality, they may be reluctant to come forward and give their details," says Paul Davies, the national wheel-clamping manager for the DVLA. Indeed, according to police it is a common tactic among criminals to buy a car at auction, not register ownership with the DVLA, and used it as a 'pool car' for various criminal activity.

The DVLA pound in Phoenix Street, West Bromwich, is one of 22 such sites around the UK. Each day, dozens of untaxed vehicles are brought in from across the West Midlands each day, and there are about 200 cars on site at the time of our visit. The back of the yard is for the new arrivals, where they will be held for seven to 30 days, depending on the circumstances of their confiscation. If they are not reclaimed within that period, they will be earmarked for disposal, and either sold at auction or sent to the crusher. A fenced-off area in the middle of the site holds the cars which are ready to be sold.

"Nationally, we clamp 10,000 vehicles a month, and 70 per cent will pay at the roadside," says Mr Davies. But of the 3,000 that will be taken into the pound, only a small number are ever reclaimed.

"It often tends to be the older vehicles that are brought into the pound, and it costs more than they are worth to get them back."

According to the DVLA, around 1.9 per cent of vehicles on the road are untaxed, at a cost to the taxpayer of £120 million.

Last year, enforcement action was taken on 52,073 vehicles in Birmingham, more than half that in London – despite the capital having a population eight times that of the second city.

In Dudley, 9,631 vehicles were clamped for unpaid road tax last year, compared to 4,138 in Telford and 5,424 in the rest of Shropshire.

Jo Halfpenny, who has been an enforcement officer for about 12 months, says she typically clamps anything from 10 to 20 vehicles a day.

Mr Davies, who has worked with the DVLA's enforcement team for about eight years, makes no apology for his work, and says the majority of people are supportive of what he does. The DVLA's enforcement teams bring in about £32 million a year through fees and income from vehicle sales, considerably mitigating the revenue lost to evasion.

He says his teams adopt a firm-but-fair approach to people who have not taxed their vehicles.

"Sometimes, if they haven't had the opportunity to tax their vehicle for a genuine reason, we will release the vehicles free of charge," he says.

"Some people do forget, and we appreciate people have busy lives," he says. "We do send out reminders, and last-chance reminders as well. Vehicles can be taxed online 24/7, so there's really no excuse.

"Ninety-eight per cent of people comply and tax their vehicle. Why shouldn't the other two per cent?"