If we take this as true and IR35 has affected these drivers so directly then what you're looking at is a huge group of non-employed independent contractors, all "employed" to one employer but making a bit more dough because they're getting paid as a limited company.
So that's kicked in, the drivers have baulked at the PAYE drop in wage, as the firms have decided to put them back onto their payroll but tried to levy the supposed direct payroll costs back onto the workers. It's happened to loads of lads I know over the last couple of years- myself included- and I can't blame them for not wanting to stay in the game- or working less via PAYE- if it's a transfer from making bags of money as a LTD then getting turned over.
Quite weird if the advent of Brexit ends up kicking in a batch of workers rights but I find it quite unlikely to be honest
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Self-driving freight lanes sound fucking scary tbh keep me well away from that shit.