Actually given the fact that the Launch of missiles at London would pretty much cause M.A.D...

Mathew's probably going to reduce the human world to ashes. Which is fine by Bedivere's standards. Vampire will rebuild society upon the ashes. Camelot is protected by Merlin's wards and foresight. Hence he wouldn't really care if the UK gets forced into a world conflict ending in the nuclear apocalypse. The man after all, is a relic of times past, a sword in the days of warheads. Do you seriously think he has any care for what happens to the world should Mathew decide to attempt and destroy the UK?

Nope. In fact, it's all the more excuse he needs to attack France.