Plunger
Appears the Bristish staff have been made redundant and foreign staff employed to replace them. I might be wrong, but I thought if redundant the position no longer existed. You couldn't make someone redundant then employ someone to do the exact same job. Also you can't sack someone arbitrarily you need a valid reason eg poor performance with minuted meetings as a warning.
I don't know the nationality of the replacement workers, although I read (not sure it's true) that some of them are likely to be Columbian.
It's not really relevant what nationality they are.
P & O has been able to sack the British workers because their contracts were signed in Jersey, which means they're not covered by UK laws. In any case, there are ways of getting round "fire and hire" practices - much more difficult in the EU.
Unfortunately, "firing and hiring" is possible and much more common than people think. This is what libertarians, such as Patel, Sunak and Rees-Mogg, have been advocating for years and why they disliked the "constraints" of the EU. Unfortunately, they were supported by the RMT pre-referendum, so I'm not impressed with the RMT's current hand-wringing.