Police tracked Keith Young to a car park on the Horseshoe Pass, near Llangollen in North Wales, through his telephone, but were too late. The 38-year-old farm worker from Winsford, Cheshire, had already carried out his threat.

A dog handler from North Wales Police, who was first on the scene, smashed the windows of the four-wheel-drive Mitsubishi Shogun and pulled the boys’ bodies from the back seat, but they were already dead.

Their mother, Samantha, 27, who separated from her husband shortly before Christmas, went to Wrexham Maelor Hospital yesterday to identify her children: Joshua, seven, Thomas, six, Callum, five, and Daniel, three.

Mr Young had collected the boys from the Handley Hill Primary School, in Winsford, on Wednesday afternoon, as arranged with his wife to give her a break. She became alarmed when he failed to return them to their new home in nearby Weaverham at the agreed time.

It is understood that she tried to contact him by telephone but it was not until midnight that he returned her call. He told her that he was going to kill himself and the boys, who were in the car with him.

Mrs Young telephoned the emergency services at 12.20am, saying that she feared for the safety of her children but did not know where they were. Cheshire Police tracked Mr Young’s mobile telephone to the remote hillside beauty spot and sent a helicopter in pursuit. The dog handler found the car at 1.37am, an hour and 40 minutes after the initial call, close to the Ponderosa Café, a well-known stop for tourists and daytrippers.

All the doors of the H-registered vehicle were locked and the windows sealed. Mr Young had rigged up a petrol-driven lawnmower in the back and set it running.

Deputy Chief Constable Bill Brereton, of North Wales Police, said: “My heart goes out to the family. It is bad enough to lose one child, but to lose four is horrendous. Clearly the officers who arrived on the scene did their best but in 29 years of police service, I have never come across anything like this.”

Mr Young was well-known in Winsford and was regarded as a “jolly” personality. He worked as a farm labourer, mostly on his father’s farm. He and his wife had lived together for some years before marrying in June 2001 at a local church.

Neighbours said that the marriage had soured quickly. They spoke of rows and incidents of domestic violence. Mr Young had been hot-tempered and emotional. Mrs Young took the children shortly before Christmas and moved to Weaverham, six miles away. Mr Young had continued to live at the family’s red brick, semi-detached house, but was said to have become increasingly depressed.

Sheila Langley, 42, a shop assistant who spoke to Mr Young and his youngest son, Daniel, on the morning of the tragedy said that he had not been his usual self. “He wasn’t as jolly as usual. He came in with his youngest, Daniel, buying pies and sweets. The others were at school. I knew he was devastated at Christmas about the split.

“He was a jolly, jolly man. He was always pulling your leg. I knew he had lost lots of weight. It was a turbulent marriage. He was devoted to them.”

She said that Mrs Young had also been into the general stores in the afternoon. She had seemed quite happy. “She said something like she was having a bit of peace because he had got the boys. Little did she know.”

Tom Challoner, a neighbour, said that Mr Young idolised his sons and had often given them rides on a tractor round the fields. “They were smashing kids and could always been seen playing in the street,” he said.

The children spent some time at Wallerscote Primary School, in Weaverham, before moving back to their old school, Handley Hill. Steve Roberts, headteacher at Wallerscote, said: “They were lovely lads, popular and well-liked, literally little peas from the same pod.

“The eldest boy was always looking out for his brothers. Although they were not with us for too long, it was long enough to know that we will all miss them a great deal. No words can adequately express the total shock and devastation we are all feeling and our hearts go out to their mother and family.”

Jill King, headteacher of Handley Hill, said: “They were lively, chatty, lovely, never any trouble at all. They were just a joy to teach, always very friendly. I can’t believe that we have just welcomed them back into our school community. When we have had proper time to grieve we will be finding a suitable way to commemorate them.

“I can’t imagine what their mother must be going through. She thought the world of her boys and as far as I’m aware their father did too.”

A post-mortem examination carried out last night showed that the boys and their father died from carbon monoxide poisoning.

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