After getting the PDC error diagnosed this morning and getting an unrequested and unmentioned (until I commented that it looked like it had been washed) wash by the BMW dealer (despite telling them last time not to wash it) I had a quick check on the forecourt and couldn't see any scratches on the bodywork.
However, after seeing it tonight under the harsh lights of the company car park, it now appears they have put almost as many scratches back in as I've just had removed.
The car had not seen a mitt/sponge since it was detailed, and has only been foamed & rinsed since, so I know I've not put them there.
Now I've got the challenge of getting them to sort it out.