CAP 393 Air Navigation: The Order and the Regulations
Section 2 Page 9
(6) Subject to paragraphs (2), (3) and (4), if two or more flying machines, gliders or airships are
approaching any place for the purpose of landing, the aircraft at the lower altitude shall have the
right-of-way.
Yes, the joining aircraft falls foul of that one too; unless you mean it's acceptable to join at low level and barge in? No, I'm sure you don't!
