I'm not sure how many people commenting on this thread have maritime experience. I have a decent amount, having worked for my whole career as an officer at sea and a manager ashore in a shipping company, including some time in P&O Ferries, and Irish Ferries who had a similar situation to this many years ago.
For those who's experience is all ashore, here are some points of interest. I'd like to point out I really, really dislike what P&O are doing here, including to some friends, but I think it will be useful for you to get some further background
Like it or loathe it (I'm certainly loathing it), what P&O are doing here is almost certainly legal.
- The legislative framework at sea is completely different to ashore
- I am pretty certain (though can't find the exact piece of legislation) that there is no need to consult before a change of this nature under the Maritime Labour Convention. This isn't redundancy, it is a simple end of contract. Like it or not, that is allowed under the MLC.
- RMT are clearly equally certain that P&O are probably on a decent legal footing - the reason they are telling their crew to remain on the ship is that it is the last hold they have over P&O - as soon as their last member gets off the ship they have lost.
- P&O are a major company with good legal advisers. They wouldn't have done this unless certain it was legal.
Agency crews are common. Getting 800 new agency crew is a bigger task, but far from impossible. There are 1.6 million seafarers worldwide, and it is a genuinely worldwide labour market
Ships changing hands, getting 100% new crews, and going straight back into operation is surprisingly common. There is legislation to cover it, but it is entirely possible to do that safely and legally within a few hours. I have been involved in taking over a ship from another company, and it took about a week to get going, but that was in far more complex circumstances. In these circumstances, with enough planning and the right people, I would have been confident to be able to pass MCA inspections and sail today (though I must emphasise that I would never have done it like this for moral reasons). The most complex area is the engine room, but it is achievable. I'm a navigator, and I know that I could have got the bridge and emergency response organisation up and running in that time, and have talked to Chief engineers who have made it work below. Insurers know this well, and are happy with it