I know from experience how keen they are on making you wear the reflective on a night. Three times me and another rider got told to put our reflective jackets on. It was not the fact that I did not want to wear it, but there was more than an hour at least till sunset, no where near dark and it was roasting in the heat. Just to keep the motorcycle rider happy, as he was shouting at us and waving his arm wildly on the last occasion and told us he would not tell us again we stopped and put them on. To try and keep cool, I just removed my jersey and stuck it in my saddlebag and wore the reflective jacket till it cooled down a bit. But, I did hear afterwards that there was an over ambitious motorcycle rider who had a go at a few riders in similiar circumstances and we must have come across him.
Plus, not wearing one could incur a time penalty, think its a couple of hours, plus they might have added another hour or two for ignoring a marshall as well.