Plenty of mileage in this issue for debate. One fundamental point is .... What is this Anglo American World Power ? Do you see it in the news? Do the two nations act together as one?
There may have been a duality during World Wars One and Two, but since then I cannot see it. A few points off the top of my head :
They did unite militarily to invade Iraq, although a lot of Brits were against the action.
They are both in NATO and they do have a “special relationship “ , but this does not stop disagreements
They cannot agree on the deportation of wanted suspects of crimes
There is not a special trade agreement in place , although this has been suggested, post Brexit.
Most citizens of Both Britain and the USA would be annoyed at the suggestion that they were merely a part of the other’s world power.
I have not seen any references to the existence of such a thing apart from the WTS. I contend that it does not exist and has not existed since at least 1945 .....