Simply provide some contact details and a panel of UK equine trailer insurance providers will contact you directly. Meaning you can compare multiple insurance providers without having to put in the work of trawling around websites trying to insure your horsebox.
An equine trailer is just another term for horse box along with horse van and horse float (in some parts of the world). The can vary massively in both size and design but the principle is the safety and comfort of the animals during transit.