The UK Trident programme encompasses the development, procurement and operation of the current generation of British nuclear weapons, and the means to deliver them.
Trident itself is an operational system of four Vanguard-class submarines armed with Trident II D-5 ballistic missiles, able to deliver thermonuclear warheads from multiple independently-targetable reentry vehicles (MIRVs). It is the most expensive and the most powerful capability of the British military forces.
"The common threat, to Russia as well as Britain, is violent Islamist terrorism. Neither Isis, nor any other extremist group of terrorists, or any other foreseeable enemy, is going to be deterred by Trident. Yet the government next year will ask MPs to vote on a new system which the Tory chairman of the Commons foreign affairs committee, estimates will cost £167bn over its lifespan."