I think that super power affiliation is perhaps a somewhat outdated definition of the three worlds concept and Britain certainly doesn't fit the modern one [1]. This guy argues that Britain is best thought of as a fourth world country [2] and he explains why the financial markets now compare Britain to a banana republic [3]

[1] https://en.m.wikipedia.org/wiki/First_World

[2] https://eand.co/how-america-collapsed-and-became-a-fourth-wo...

[3] https://eand.co/britain-just-hit-the-next-level-of-self-dest...