Dog-walkers are being warned to keep their pets on leads after the suspected poisoning of a family pet.

Ian Henderson said his three-year-old retriever Cloud fell ill within hours of returning from a walk in Withdean Park, Brighton, and died the next day.

Mr Henderson, of Graham Avenue, Withdean, said: "He was running around happily when we got home but, within an hour, he was fighting to breathe and his back legs collapsed.

"Whatever it was that killed him must have been strong because Cloud was such a big dog.

"I'm worried about what could happen to children and other dogs if they found any of this stuff. I think dog walkers would be better keeping their pets on a lead."

Cloud was running off the lead into copses as Mr Henderson walked on the path during a morning walk in the park, off Peacock Lane.

He had not been off the lead anywhere else that morning.

Mr Henderson's wife Bev said: "Cloud would never go far because he was cautious and always had to be able to see us. We have seen dead rats in the park a few times in the past months, as have others, which makes me feel he must have eaten something poisonous."

A vet told the family that Cloud had probably been killed by a substance similar to that found in rat poison or weedkiller.

A spokesman for Brighton and Hove City Council said pest control departments had not used chemicals in the park.

She said: "We don't know where this could have come from if the dog did pick something up. Environmental health officers are investigating."