Dr Michael Mosley investigates Britain's most secretive and controversial military research base, Porton Down, on its 100th anniversary. He comes face to face with chemical and biological weapons old and new, reveals the truth about shocking animal and human testing, and discovers how the latest science and technology are helping to defend us against terrorist attacks and rogue nations.

Lying on the remote north west coast of England is one of the most secret places in the country - Sellafield, the most controversial nuclear facility in Britain. Now, Sellafield are letting nuclear physicist Professor Jim Al-Khalili and the television cameras in to discover the real story. Inside, Jim encounters some of the most dangerous substances on earth, reveals the nature of radiation and even attempts to split the atom. He sees inside a nuclear reactor, glimpses one of the rarest elements in the world - radioactive plutonium - and even subjects living tissue to deadly radiation. Ultimately, the film reveals Britain's attempts - past, present and future - to harness the almost limitless power of the atom.