I decided in the moment that if I had done anything this morning, the local force couldn't know about it yet, so I stood still. It turned out not to be me they wanted, but the other two lads, and the previous shouting was followed by a round of "Drop the bag" to them, and "Move on quickly" to me. At least they didn't try "Nothing to see here," which was patently false, although by that time I wasn't in any mood to hang around.
The girls in the flower shop on the corner were very kind a few minutes later, and said I looked terrified. I suppose I must have done.