I don't care who you are, if you are in my reserved seats I will ask you to move.
People reserve seats for reasons that are their own. On booked trains its rare to find every single seat booked. The couple could have easily found a couple of seats together. They did not need those table seats. If both required seats they could have approached other people on the none tabled seats.
I have also been on trains where reservations have been cancelled because of fewer coaches. Did I sit in the first table seat halfway down a carriage? Nope, I either sat in a none reserved seat or found help from staff.
There have also been rare times when there's been an error and the seat double booked. Did we sit there, nope we worked together to find a solution on a very packed train. Which I really doubt this one was, because usually packed and reservations cancelled means people are standing on carriages more than this one person.
And why are people paying to book their train tickets in the UK? It's free for everyone. Just ensures you have a seat, well unless you do meet entitled fuckers.
@AthollPlace I have in the past put a toddler on the table, and didn't do the usual reminder about people and being nice. I was that parent who thought all that annoying stuff was amazing, and just exploring their environment. Got a couple of chuckles when I said along the lines of and today their interactions include a couple of gate-crashers, who are such silly billies who would rather be stubborn and stay, instead of seeing some other lovely people. And everyone would travel happily and comfy.