Althought Trident is costly, whilst we have Iran, who are striving to produce war grade plutonium to produce a nuclear war head, and North Korea, who already have a nuclear weapon, the world is not a safe place. Far better to have a nuclear weapon at our disposal, rather than none at all. Trident is no longer a deterrant - it can be use as a first...strike missile, or it can be used in retaliation.
The cost of ending the production of the Trident war head would run into trillions of pounds. And for those who want to get rid of Trident, I suggest that they please do inform us of what they would do with the exsisting nuclear war heads, the manufacturing facilities, the storage facilities, etc?