To my amazement, I've found that homing works, and probably did from the start. I just didn't understand how G28.1 was supposed to behave. I'm sure I tried to read up on it prior to starting this little escapade, but I didn't understand the significance of the number after the axis letter.
I now realise that
a) Home switch will not trigger until axis is in its 'slow zone'. This information is not in the config manual; I have a stretched drive belt and a broken home switch now due to not knowing about that.
b) That the number after the axis letter denotes the point at which that slow zone will start. (Says so in the manual, but not clearly enough for me apparently)
I'd been trying to trigger the home switch with the axis 'out of step' by +/-50mm (simulating massive loss of steps), but with the slow zone setting at 1.00, and only using G28.1 X0, instead of slow zone of 50, and G28.1 X100.
I'm not blaming the author of the manual, it's my fault for not understanding something properly before using it.
I still need to have homing like behaviour on my Z axis that moves in the opposite direction to homing proper, so I'll still try a macro/macropump to achieve that, as in one of other current threads.
I think this may mean my problem is solved, we will wait and see...