I didn't say that Brexit hasn't had an effect on the number of HGV drivers working in the UK but it's misinformative to infer that it's the sole cause.
The haulage industry estimates that there's a 100k shortage of drivers, from [ref]Flyingfifer[/ref]'s stats above there's been a net loss of approximately 13.4k EU drivers - taking those figures, Brexit may have accounted for up to 13.4% of the current driver shortfall. This may have been enough to turn a 'just about coping' situation into a 'shitstorm' situation but the straw that broke the camel's back is never the sole cause of its fractured spine.
It's a problem that seems to have been building for years, there aren't many people who want to spend days on the road, sleeping in a truck cab, away from friend & family. It probably won't go away until fully automated trucks are allowed on the roads.