Very many thanks to all those who answered part 1 of this question see here
The regex that worked for me was
(?<![A-Z]\s)\b[A-Z]+\b(?!\s[A-Z])
The question now is how to do the inverse, i.e. given the string
This is a different sentence WITH a few CAPITAL WORDS here AND THERE ACROSS multiple LINES.
How to match "CAPITAL WORDS" and "AND THERE ACROSS" but not match "WITH" or "LINES" as they are isolated with lower case words either side, or they could be at the end of the start of a sentence.
I tried changing from negative to positive lookarounds and altering the [A-Z] to [a-z] but again failed spectacularly
Any help would be much appreciated once again.