DVLA have mobile enforcement units just cruising the backstreets in normal times. These are just discreet vans with minimal signage and a couple of small ANPR cameras mounted on the roof. If you are not observant you might just dismiss them as the van of a tradesman and they drive around waiting for the cameras to get a hit, at which point they pull over and slap a wheel clamp on the offending vehicle.
Highly amusing for a law abiding vehicle owner like me..... It's not like taxing a car is difficult nowadays, with email & postal reminders and auto direct debit renewal. That is of course assuming you intend to pay....