I don’t think it’s that simple, to come and actually work in the UK for a UK company, an EU national (without prior rights) needs formal permission to work in UK, much like an UK citizen working in EU.
These were FTSE100 companies with subs across Europe, consequentially people would be ’employed’ by a local business, but working across the business – so working out of London I ’employed’ folk in France, Germany, Spain etc, but we all worked across Europe (and the RoW).
And the EU citizen can come to the UK for twice as long as we can go to ANY of the EU country’s.