RCX, what would make it illegal?
Normally the steering wheel would be strapped in the straight ahead position, but most cars steering column locks in the ahead position, not recommended to rely on the steering lock but possible.
If the car is in gear the recovery driver will soon feel it, a rear end lift is not usual depends on the cars condition/damage.
I can't see why the vehicle couldn't be legal here, there's plenty of American commercial recovery trucks in England, it has English vehicle registration plate numbers.
PS. The only thing l can see that is illegal, is the towed vehicle is not strapped to the
tow truck and there's no towing board fitted, but that the drivers fault not the tow vehicles.
Done properly.
Few vids ahead of the link posted originally.

A few reasons I'd think it's illegal. It's easy to cause damage if the car is in gear. You just don't know the status of the car, what if it has a transmission brake and you're pulling against the brakes, overheating them and causing microfractures. Plus our towing laws are pretty strict and the car is still on the ground. And videos of similar trucks show that the car being towed often slips off.
It was this video that made me think there's legal issues, skip straight to 3:07, you can see the car is being pulled against it's transmission, and then falls off the rig. There's a whole string of video of this same tow company and the cars keep falling off and they don't care:




