The Beefeaters (Tower Guards, a.k.a. Yeoman Wardeers) are friendly but are definitely still members of the military- they carry AK-47 automatic rifles fitted with old-fashioned-looking bayonets. 

When Greg asks about the old flags hanging in the chapel, one says "You Americans have 'flags' and bad habits; we English have 'colors' and traditions."  The flags, by the way, were carried by military units taking part in past campaigns; the flags hang in the chapel and cannot be taken down until "not one thread holds the color on the staff."