May  UTC   Ah now this is a very interesting question especially having in mind a curious concept in the unwritten constitution of the UK that of the Crown and royal prerogative  through which ministers including the Prime Minister derive their executive authority The Prime Minister acting in his capacity as a crown officer can ask for a nuclear strike However the Prime Minister unlike the President of the US is not a commissioned officer in HM Forces and therefore cannot order any serving member of the armed forces to do anything and require them to obey Instead she will ask the Chief of the Defence Staff who is a commisioned officer to order the launch This in theory provides a safeguard against a particularly despotic Prime Minister going rogue and ordering a nuclear strike on their own In practice however it is unlikely this distinction would be observed  especially in a crisis situation likely to require nuclear retaliation Further complications arise due to submarine based Trident weapons and the envelopes onboard This whole topic is explored in much more detail in the book The Secret State  Britain and the Cold War by Professor Peter Watkins