Originally Posted by
patvd
You mean the middle seat? That one is indeed free space to be shared between the window and aisle seat passengers, but should remain unoccupied.
In fairness, the OP specified in his first post that he meant 2-2 seat configuration. FT users rush to comment on something they did not read in detail...
Nevertheless, I still think that even in 2-2 C seat configuration, guesting someone from Y on the seat next to you is not allowed.