He'd have had to replace the ceiling if he pulled them out.
Yup, as above.
Options were...
a.) rip ceiling down, replace joists
b.) rip ceiling down, jack up, sister to retain
c.) sister joists at new level
d.) fit firring strips
I decided C was easiest given that I have to live in the house and I probably don't have the skills to do D to a decent standard as would require a bespoke cut per joist.
Updated man jobs since...
As expected, once I got the first few boards down it went quite quickly:
As mentioned, I had to leave the floorboards at the side of the room as the stud wall looks to be built on top of it, floorboards overlaid the majority was some packing but was higher near the door so bit of ply, caulk, primer and self-leveller and sorted:
And as of today, room prepped and painted, new window sill (took out uPVC overlay and fitted the melamine/chipboard type) and wardrobes in.
Even had to resurrect some kitchen fitting skills to scribe a bit of trim for the wardrobes
Just need to touch up around the trim and waiting for the carpet and blinds.