A national nuclear deterrent is only of use in deterring other nations who possess their own nuclear weapons, the means to deliver them and the ideology and intent to countenance their apocalyptic use. Can you name any?
However, there are many nations and ideologies that are capable and willing to employ lethal conventional force to further their aims and are constantly doing so.
As a nation we in the impoverished UK need carefully to balance our capability to combat both threats. It is not logical, sensible or cost effective to put massive funding into the former when it is at the expense of the latter.