The conventional wisdom is that the Cold War ended in 1991. George Friedman prefers to put the end of the Cold War in 2024 or 2025 when it became common knowledge that the Russians just didn't have much military strength.
Before Feb 2022 we didn't have any conclusive way to determine its strength, so a prudent military strategy would have been to assume that the Russian military was strong -- until 2024 or 2025, when a well-run country in Europe would have realized that it is safe to lower its defense spending (except Ukraine of course and to a lesser extent Moldova, Georgia and maybe the Baltic states and Finland).
The UKs threat from adversarys is nuclear, nearly nothing else.
Now the threats to the UKs interests abroad are larger and may necessitate a large military, of course.