Thanks for the suggestion. I just did the X test, the edges of the score came away slightly during scoring which the tape then removed, less than 1mm though.

The adhesion of the old paint seems to be the problem, I washed a new section and attempted to scrape off the bubbles as they appeared... While doing this a whole section of the paint came away, revealing a layer of blue paint. The blue paint seems to have adhered properly so it looks like the best option is to strip the whole wall of the top layers of paint