Warning: Be sure to check the rules / laws / potential fines; this could come back to bite you if you tried similar and in fact Police were called.
I was travelling from Edinburgh to London by train and had a booked window seat with a table.
I got on the train to find 4 guys sitting at the table, the one in my seat that was clearly marked as booked, refused to move as he was with his friends and the train was packed. The ticket collected passed and I asked him to help.
He asked the guy to move but he refused and somehow that was that.
“So what now?” I asked
“You can find another seat but I have no power to move him, only the police and move him and they will not turn up just to move someone out of a seat.”
There were no seats free in the carriage and probably not many free on the train so standing to London was a possibility.
“I’m going to take a seat in first class” – better surroundings, power sockets and free tea and coffee.
“You can’t sit there, you don’t have a booking”
“Well, you could call the police to move me but apparently they won’t turn out to move someone out of a seat”
I had a lovely trip with power for my laptop and a wide comfy seat.