A gundog breeder who carried out a bizarre campaign of intimidation against a couple who bought a fish farm that he wanted was last night facing a lengthy jail sentence.

Robert Walker, 50, of New Ivesley Farm, near Esh Winning, County Durham, was described by detectives as a "very clever and devious man" who had falsely branded his victims with the worst slur possible - that they were paedophiles.

A pipe bomb was also discovered at his farm when police went to question him.

During a three-week trial, the jury was told of how Walker had tried to intimidate Sidney and Margaret Boulter, from Oakbank Fisheries, in Longtown, Cumbria.

During the vicious vendetta, leaflets claiming paedophile activity on the farm were distributed, a fish-filled pond was contaminated with oil, and rat poison was sent to the Boulters' 12-year-old son through the post. When police raided Walker's farm, they found a pipe bomb, four modified flash units, gunpowder, a modified torch, milk cartons containing petrol and an alarm clock altered to act as a timing device.

The saga began in 1998 when Walker offered £190,000 for the complex and then tried to drive down the price by claiming the land was riddled with defects.

The vendors pulled out after months of haggling, and by April 5, 2000, the Boulters had offered £150,000 and contracts were exchanged. Two days later, Walker told police there was a paedophile working at the fishery.

Then on June 5, Mrs Boulter found a leaflet propped on top of a drum of diesel saying: "Get out now while you are safe".

Flyers were sent to fishing tackle shops and thrown from a car window in the community. One read: "Public Notice: Save our school kids. Paedophiles now operating at Oakbank Fisheries. We know what to do to encourage them to close now."

During the anonymous campaign, Walker continued to approach the Boulters' solicitor offering to buy the property.

He denied having anything to do with the leaflets and claimed the explosive materials were for "pleasure not for pain" because they were intended for a fireworks display.

But key evidence against Walker included forensic evidence examination of his fax machine which showed it had been used to produce the leaflets, and DNA tests which linked him to leaflets which had been posted.

After more than 11 hours deliberation, a jury at Newcastle Crown Court found him guilty on two charges of harassment and one of having explosive substances.

Later, Detective Sergeant Peter Proud said: "This case has affected me personally. It involved the worst possible slur on anyone's character - that they were a paedophile.

"This was a case of vicious, systematic mental torture on the Boulters."

Judge Tim Hewitt told Walker: "A custodial sentence of some length is obviously inevitable, bearing in mind the serious nature of these crimes."

Walker will be sentenced on October 11.