First: do not become part of the problem
A loose horse is frightened, and a frightened half-tonne animal that feels pursued does the one thing everyone is trying to prevent — it runs, often straight onto the road it has so far avoided. So the first rule for a finder is restraint: do not run at it, do not try to corner it against a fence, do not wave your arms to steer it, and keep dogs and children well back. Watch from a distance and let the horse graze or settle. A horse that is standing quietly eating a verge is in no immediate danger and neither is anyone else, which gives you the thing this situation actually runs on: time to get the right people coming. If the horse is already on or near a busy road, that changes the balance — skip ahead to the police call and warning traffic, because a settled horse on a verge and a trotting horse on a carriageway are two different emergencies.
Take the details a searcher will need
While you watch, build the description that lets an owner say 'that is mine' in one sentence: colour and approximate height, any white markings you can see, the colour of any rug, whether it wears a headcollar or is tacked up, and anything distinctive such as a clipped pattern or a brand of shoe. Note the precise location — road name, nearest junction or gate, direction of travel if it is moving — and take a photograph from where you stand if you can do so without approaching. This sounds like a small thing, but yards and police receive 'there is a brown horse somewhere near the village' calls regularly, and the finder who can say 'bay, about fifteen hands, red rug, grazing the verge by the cricket field gate' has effectively started the reunion already.
Make the two calls that matter
Phone the police on the non-emergency number, or the emergency number if the horse is on a road and traffic is at risk, and report the location and description; they log loose-horse reports precisely because owners phone them too, and the log is often how the match gets made. Then call the nearest livery yard, riding school or feed merchant you can find — local horse people know each other's horses, and a yard will frequently send experienced handlers with a headcollar and a trailer while a finder is still deciding what to do. If you belong to any local community group, a post with the photo and location spreads fast, but treat it as the third call, not the first: the people physically closest to the horse matter more than the widest audience.
If you are confident and the horse is calm
Some finders are horse people themselves, and for them a calm catch is reasonable help: approach slowly at an angle toward the shoulder, talking in a level voice, and let the horse close the last distance to a bucket, a handful of grass or an outstretched hand rather than reaching for its head. Slip a rope or a belt around the neck before attempting a headcollar, stand at the shoulder, and lead from there. Never wrap a rope around your hand, never stand directly in front of the horse, and if it is wearing tack, do not be tempted to ride or tie it to anything that can move. If the horse will not be caught but is contained in a field or lane end, simply guard the exits and wait for the yard's handlers — containment you can hold beats a failed catch that puts it back on the road.
The fastest route to the owner
However the catch goes, identification closes the job: check for a contact number on a headcollar disc or rug tag, and if the horse carries a KinsLe QR tag, scan it — KinsLe's Verified QR ID Pet Profiles give every pet a unique QR ID, and the scan opens the horse's profile and the owner's contact details, turning hours of phone calls into a conversation you can start on the spot.