Root cause
You can trace the root cause of this incident back to at least 1987.
When I was working as a PDI engineer at LHR Terminal 1 'the management' decided that there would no longer be an engineer attending departing a/c and that the only PDI would be done by the flight crew as they did at the outstations.
As an engineer I was equipped with a suitable pair of overalls, and a 'GS' screwdriver to insert in the gap between fan cowls etc and try to lever them apart. I was also given the time (while the fuel went on) to have a proper look around. We even had a tumble dryer in the crew room to dry the knees of our overalls, which was used frequently.
So 'the management' decided that the best 'bloke' (as it was in those days!) to kneel on the wet tarmac and check the low hanging cowls was a chap in a suit with no tools or protective clothing. This chap would then have to sit in the flight deck for the next few hours in a damp suit...
When I joined the Aircraft Maintenance Industry in 1979 I was taught about Murphy's law that states 'if it can go wrong it will go wrong'. This is why a/c and maintenance system are designed to make sure it doesn't go wrong.
If one of my colleagues on a long wet night shift didn't close the cowls etc there would be a good chance I would catch it on my walk around, and then there was still the flight crew walk around. Plus any previous comments in the Tech log, which would be be a good indication of possible problem areas.
It doesn't take a rocket scientist to work out what removing the PDI engineer might lead too.
So BA, I know you monitor this forum closely, before you hang an engineer or pilot out to dry (excuse the pun!) just remember the management decisions back in the 1987, and all the money you saved!
I was that angry young man in 1987 telling you what a bad decision it was.
You know who you are...