Remember, when you are designing the uniforms for your personal guard, style and color counts! Stormtroopers may look cool in the movies but you're going to have to look at these guards every day as they mill about your hollowed out volcano. So choose wisely.
These are the Beefeaters, or "The Yeomen Warders of Her Majesty’s Royal Palace and Fortress the Tower of London, and Members of the Sovereign's Body Guard of the Yeoman Guard Extraordinary" *gasp*. Which is a ridiculously long name and probably why everyone just calles them "beefeaters".
They guard the Tower of London and keep Her Majesty's ravens. You know the guards belong to her because she writes her name on everything. "E II R" is Queen Elizabeth's royal cypher and translates as "Elizabeth the Second, Regina".