Originally refered to English cricket supporters traveling to Australia to watch the ashes series in 1994/95. Barmy because of all the money they spent to get there to warch a team who had no hope of winning (they didn't). Army because of the 100's of them who would all sit together, cheering on and supporting the team.
It is now generally used for any large group of English cricket supporters on tour anywhere in the world. It can occasionally be used to include other English teams - It's use for rugby is just about acceptable but certainly not for football.