Compensation culture gone mad! I learned to ride in Lincolnshire and there were some pretty large aircraft flying about from Waddington at the time (Nimrod AEWs and visiting fast jets). The horses were fine. Would horse owners sue car and wagon owners for spooking their horses whilst on the roads?
I've heard some pretty miserable low flying stories over the years (and that's what most are - stories). Flying causing subsidence, chimney pots being knocked off houses, many of them unsubstantiated by thorough investigation. Instead of running to court and suing, how about a little investigation as to frequency of flying and the effect on the animals?
After the Bell case in Lincolnshire (a rider was killed after her horse was startled by a Chinook in 2003) the MoD had safety trials and, working with the British Horse Society, began issuing high vis jackets to horse riders so that pilots could pick them out and take evasive action. I believe the scheme started in Scotland first a couple of years ago. Has the horse owner contacted the Society for a jacket?