Well.............
Turns out my initial diagnosis of dodgy low pressure fuel sensor was correct.......
However, the sensor I bought to replace the dodgy sensor, was dodgy, ffs........
As above I would have not bet on that.
Anyway, lesson learned here, make sure you get get good quality/genuine sensors. I cant say I have ever had an issue before this was the first time, but I guess when you are dealing with a fuel system that has something like 8 separate components working together, buying a cheap sensor doesn't necessarily eliminate the problem, and on this occasion created a rabbit hole that never needed to be......
At least its sorted now.