The 19-year-old, who had only served eight months, was killed on 17th May 1978 with his own truncheon and a brick after chasing a suspected burglar.

Now, three decades later, Christopher's mother Joan (71), who still lives in Skegby, remembers vividly the events of the day her son died.

She told Chad: "I can still play every moment of the day in my mind and I will never forget it.

"Thirty years is a long time but I still find it upsetting when I think about how Christopher died, probably even more so recently because it is a poignant anniversary and many people have mentioned it to me."

Joan, who lost her husband John five years ago, is now on the judging panel for the Nottinghamshire Police Officer of the Year award.

"To think that if Christopher was still alive he may have retired from the force this year is unbelievable," she added. "It is amazing how fast the time has gone."

Pc McDonald had responded to an alarm at a jeweller's on Central Avenue in Worksop during his night shift and at the scene, he saw the suspects and chased them.

While other officers were on their way, Pc McDonald called in to say he was in contact with the suspects.

But after sending a further message of their whereabouts, nothing was heard from him and following a search, his body was found later that morning in the river, just 200 yards from the scene of the burglary.

Later that day, 20-year-old Peter Loveday was arrested and subsequently convicted of murder and sentenced to life imprisonment.

Pc McDonald was posthumously awarded the Queen's Commendation For Bravery in 1980 — one year after the Christopher McDonald Trust was set up.

Each year, selected officers benefit from the trust by taking part in an outdoor pursuit training and educational scholarship to encourage teamwork and personal reflection.

Chief Constable Steve Green is currently running more than 180 miles between every police station and contact point in the county to raise money for the trust.

He said: "On the night Christopher died he came on duty and went out there and did his job."His life was tragically cut short, but the example he set to others continues to have a remarkable impact on everyone who hears his story."

• Anyone who wishes to make a donation to the Christopher McDonald Trust should call 0115 9670999.