Niknak is on the money. Get a broker, a good one, make sure he is licenced to do business at Lloyd's or has a good connection that is. Lloyd's has a very active war market and syndicates are often more able to spread the risk than some of the smaller insurance companies, many of whom won't touch war risks at any price.
Unfortunately one has to remember that insurance is not a profession, it is an industry and as such is there to make money, period. To get lower premiums or better cover the MOD are going to have to subsidise and that seems unlikely.