Quick update:
I haven't been driving the car much until yesterday. Armed with a more accurate pressure gauge, I discovered my pressures were 36psi on the fronts, and 52psi (!) and 44psi on the rears. 52psi was the left rear wheel with the screw.
From my conversion from bars to psi, that's about right. Except the severely over-inflated wheel with the screw. I can't believe they delivered the car to me this way.
The good news is the pressure really hasn't changed since I removed the screw, some driving may affect that. So for now, I've corrected that tyre from 52psi to 44psi, reset the TPMS and we'll see how I go.
The drive to work this morning suggests there is much less 'hopping' over corrugated surfaces. Who would have thought! Anyway, fingers crossed!