During times of ultimate duress, when the the threat level is deemed an potential extinction level event, the Pendragon Directive allows a member of the Round Table to ascend to the Siege Perilous to assume command of the British Crown and absolute authority over the Houses of Parliament, Armed Forces and civilian resources as are required to ensure the survival of the human race. Such Round Table member, by default, should be a member of the Order of Avalon.
Once the threat has passed, the Directive requires that executive function is returned to whatever Crown or civil authorities as might remain.
The Pendragon Directive is part of the UK Official Secrets Act, Section III on Earth-40. Section III is classified as secret by the terms of Section I & II and even knowing of its existence without having signed Section III, which places one under oath to the Pendragon Directive, is an offence punishable by… Well, let’s not test that, shall we?
Having felt the “breath of the dragon” an operative is under geas to safeguard the human race against supernatural, existential threats above all other loyalties and concerns. They are also compelled to not spread knowledge of the occult except where the recipients are themselves under the Pendragon Directive, or it is required as part of efforts to offset an existential threat. It is recommended that operatives do not test the bounds of these geasa, as there are more than a few examples of operatives who have tried to play fast and lose and either died of an aneurism, gone hopelessly insane or, in one notable instance, being pulled through a mirror, never to be seen again. It was a really small mirror, too.