People need to read the T&C of their policies. I also have to wear high viz gear whenever I take hprses on the road otherwise my insurance could be invalid!
Yep. If my horse is out on the road and not wearing 'at least two reflective leg bands' we are not covered either. I was out in my lorry yesterday and a big dark bay was almost invisible hacking up the road - had his rider not been wearing a fluorescent yellow coat. I think leg-bands would have helped confirm the presence of a horse underneath her!
I think that whether your insurance policy states it or not any deviation from the 'norm' is going to get you into trouble if you try to claim. I know (from experience) that they will do anything to get out of paying for a claim particularly a certain insurance company (not naming names for obvious reasons!!)