Sorry to be a nuisance, but all I am after is an answer to a) the best way to fit the sensor and b) if it is best fitted before or after completing the calliper fit. But I am receiving two versions of the procedure, one a number on here, plus Haynes, recommend, and others the one of fitting to the pad before fitting the calliper.
As I say I have tried what you are suggesting KillerWatt, but the calliper will not go over the pads in place without being obstructed by the top L of the sensor in place on the inner pad.
I think now I will just try to do it the best way I can using my experience and the advice everyone has kindly given.

Thanks all

First off Lizzie, if you don't know the answer then you ain't being a pain.
Second, maybe I ain't explaining it well enough....so I'll try again for you.......
Take one of the pads (any one you like).
Place it on the floor (bottom edge down)
Push both ends of the anti rattle spring down as far as you can
Get a second person to drop the sensor in to place
Feed sensor plug through aperture in caliper
Pull enough of the cable through so you can locate pad in caliper bracket without the cable being crushed
At this point, refer to Haynes (assembly is reverse procedure of dismantle).
But seriously, if you are stuck then I will quite happily show you how it's done when I visit the parents in a couple of weeks.
If you are going to continue and try yourself, then stop giving Vx £18 for the sensors, because CAF sell both sides for £9 inc VAT.