Tina Brown was riding Merlin when he bolted as they passed temporary metal railings on a path in Station Lane, East Ardsley, near Leeds.

She brought the horse under control but he then fell to the ground, screaming in agony with blood coming from his mouth.

Contractors for Leeds City Council are installing kerbs along the pathway and now an investigation has been launched by the council and the Health and Safety Executive.

Merlin died at the scene as his owner and a vet waited for the electricity to be switched off.

The incident happened at around 4.20pm on Wednesday this week.

Ms Brown, 54, who runs the nearby Foxholes Animal Hotel, said: "Merlin bolted forward and galloped off. I thought he'd been shot or something by his reaction.

"I eventually managed to stop him and got off.

"Then he groaned really loudly, his legs buckled and he slumped against a lamppost and crumpled to the ground.

"He started screaming, I've never heard a noise like it.

"He must have been in such pain."

A distraught Ms Brown phoned a friend and a vet. She said: "We couldn't move him because he was putting shocks into us. My friend tried to take the bit out of his mouth but the shock threw her to the ground.

"The vet, thank God, managed to put a sedative in him so he was unconscious.

"Merlin had his steel shoes on so the current must have gone up his legs. I got nothing, but I was on a leather saddle and wearing rubber boots."

A council spokesman said: "We are saddened to hear of this matter and are looking in to it as a matter of urgency."

She said highway improvement works were taking place on behalf of the council in the road.

The Health and Safety Executive say the investigation may turn into a criminal investigation.