So call me a crackpot if you will but this theory that I have sounds like it could be on point..
Bare with me. So your a haulage company who had lost a lot drivers from abroad that went home or can't get visas, so you can't pay minimum/lower wages to your drivers you see this as Brexit effecting your profits, not that your actually paying a living wage for a driver.. You still have plenty of drivers from the UK that are driving and learning. You obviously don't have as many as before so you can't send out as many as you'd like to make more money to cover your increase in wages.
Your currently making a profit more inline with what you should be paying anyway but your not happy about this and want to solve it, what do you do?
Create a panic over a non existent shortage of petrol at pumps, which in turn makes people buy more and thus put up demand, which in turn puts up the need for petrol trucks beyond what is the common average, and thus the need for drivers.
Now blame the government and propose that you need overseas drivers because we lack the staff, but actually it's because you want a cheaper workforce to increase your profit margins.