As far as Trident replacement is concerned, I'm agin. However, while it is certainly true that they money involved could be used to a far greater purpose, in the short term, the cost cannot be spoken of in simple Dollar terms alone.
What would need a great deal of pondering is our (the UK) continued place among the Permanent Members of the UN Security Council.
[Below I give the main Wiki link, the embedded links on that page will take you on.]
United Nations Security Council
"At the UN's founding in 1946, the five permanent members of the Security Council were the French Republic, the Republic of China, the United Kingdom, the United States, and the Soviet Union..."
"Veto power reform
Various discussions have taken place in recent years over the suitability of the Security Council veto power in today's world. Key arguments include that the five permanent members no longer represent the most stable and responsible member states in the United Nations, and that their veto power slows down and even prevents important decisions being made on matters of international peace and security. Due to the global changes that have taken place politically and economically since the formation of the UN in 1945, widespread debate has been apparent over whether the five permanent members of the UN Security Council remain the best member states to hold veto power. While the permanent members are still typically regarded as
great powers, there is debate over their suitability to retain exclusive veto power..."
Great power
"Characteristics;
There are no set or defined characteristics of a great power. These characteristics have often been treated as empirical, self-evident to the assessor.[9] However, this approach has the disadvantage of subjectivity. As a result, there have been attempts to derive some common criteria and to treat these as essential elements of great power status.
Early writings on the subject tended to judge states by the realist criterion, as expressed by the historian A. J. P. Taylor when he noted that "The test of a great power is the test of strength for war."[10] Later writers have expanded this test, attempting to define power in terms of overall military, economic, and political capacity.[11] Kenneth Waltz, the founder of the neorealist theory of international relations, uses a set of five criteria to determine great power: population and territory; resource endowment; economic capability; political stability and competence; and military strength. These expanded criteria can be divided into three heads: power capabilities, spatial aspects, and status"
https://en.wikipedia.org/wiki/United_Nations_Security_Council#Permanent_members