You can check it on autotrader for a specific vehicle. Look at the bottom of the advert and there will be a 'running costs' menu. Look in there and it'll tell you the road tax for that specific model + year.
16 plate Transit Custom with adblue diesel 2l cost £290 for a twelvemonth. The petrol car that the apprentice drives was £360 or 380 As to whether its a flat rate for commercials, it must be linked to emissions. Also if your vehicle isn't caz emissions compliant, there's places you can't work unless you pay an extra toll, lots of special lanes and roads in cities that if you use them, you get fined hundreds. And it will only get more restrictive as time goes on.