 The four-minute warning itself was to have been injected from a special studio at Broadcasting House and been broadcast nationally on all television and radio stations when a coded signal from RAF High Wycombe was given.This studio would also have been used by government ministers to broadcast messages and announcements until the government left London late in the crisis phase (or during the precautionary period).After an attack, there would also have been a regional service tailored to local needs located in regional seats of government.