A student fell asleep at the wheel and caused a fatal crash after "partying heavily" the previous night.

Alisdair Grant caused the head-on collision with Gerry Lewis's 4x4 in East Ayrshire in March 2014.

The 21-year-old had served a ban for drink-driving before the crash.

Mr Lewis, 54, a conservationist, never recovered from injuries he suffered in the collision, with his loss having a "profound" effect on his grief-stricken wife.

The collision occurred on the A719 close to the village of Waterside.

Grant, of Kilmarnock, pleaded guilty to causing death by dangerous driving at Glasgow High Court on Monday.

He was behind the wheel of his brother's Fiat Punto at the time of the crash, prosecutor Mark McGuire told the court.

He said: "Text messages recovered from his mobile phone sent that day indicate he had been partying heavily the night before.

"Around two hours before the collision - in response to someone asking if he was fit to drive - he replied he thought he would be soon. The texts made it clear that Grant was tired."

Mr Lewis was driving his Suzuki 4x4 in the opposite direction. He was with his wife Sarah to see his widowed mother in Glasgow.

"The hearing was told as the two approached, Grant's car drifted "without warning" into the path of Mr Lewis's vehicle.

"From what Mrs Lewis could see, there was no attempt to brake by Grant. He had fallen asleep at the wheel."

The crash caused "significant damage" to both cars. Mrs Lewis looked at her husband and immediately found he was badly hurt.

Mr McGuire said: "She shouted for help, pleading for people to assist her husband."

Other drivers came to their aid before police and ambulance crews arrived. The couple were initially trapped in the car. Mr Lewis had to be cut free from the wreckage but he never recovered.

Mr Lewis - who had worked for North Lanarkshire Council for 20 years - died due to chest and abdominal injuries. The court heard his loss has been "profound" for Mrs Lewis.

Mr McGuire stated: "Gerry Lewis was a much-loved husband and family man. His wife and and wider family miss him dearly."

Judge Lord Boyd deferred sentencing for reports.