The Belgiae tribe came from an area just above Gaul, giving the area it’s modern name; Belgium. Caesar writes that they settled after several raids on England’s south coast.
The Brigantes were said to be the most powerful tribe, owning most of Northern England. It’s not known how closely they maintained their links with their counterparts in Ireland as no written records exist before the Roman invasion. They were famously ruled by the pro Roman queen Cartimandua.
The Caledonii gave their name to the highland region of Scotland; Caledonia.
The Iceni are easily the most famous of the Celtic tribes due to Boudicca’s revolt in 60 AD. Their neighbours, the Trinovantes, allied with them during the revolt.