A drug-crazed teenager who raped and viciously assaulted a lone woman dog walker at night has been jailed for 11 years.

Jack Ian Walker, 18, subjected his terrified victim – a woman in her 50s - to appalling violence during the attack in Workington, hitting her so hard she was left with a five-inch long facial scar.

As she fought back and tried to escape, he taunted her about her age, saying “quiet grandma," Carlisle Crown Court heard.

The horrific details of the woman's ordeal were outlined after Walker, who was high on a cocktail of alcohol, cocaine and valium, admitted rape, attempted rape, sexual assault and causing the woman grievous bodily harm.

Tim Evans, prosecuting, described how at 10pm on July 16 the woman, after watching Masterchef on TV, took her dog for a walk. While on an embankment near Church Street she saw the defendant, who said hello.

Moments later, he put on a baseball cap, and pulled his hood down to obscure his face. "Unsurprisingly, this worried her," said Mr Evans.

"She decided to head back home but had only taken a pace or two when he blocked her path. He said that if the dog bit him he'd knife it."

Walker told the woman nobody would ever find him - and then began his terrifying attack.

The victim tried desperately to fight him off after telling him: “Get a grip: I'm old enough to be your grandmother.”

But the teenager put her in a headlock, then pushed and slapped her before delivering the first of several powerful punches.

Describing that first punch, the woman said it was like being hit by a boxer.

Still she fought him, as Walker pulled her hair and threatened to knife her. “Eventually," said Mr Evans, “her legs went. She was seeing double and was disorientated because of the force of the blows. She went fully to the floor."

As he tried to rape her for a second time, she was yelling for help, and this was when he told her to stop shouting, saying: "Quiet grandma."

The teenager, who was trying to drag the woman to a more secluded area near some trees, fled when he realised police were arriving – thanks to a call from a passer-by.

Officers found the woman sobbing and distressed.

She said he had never known pain like it. Turning to the aftermath, Mr Evans said the woman was left scarred and traumatised.

She told police: "Every time I look in the mirror I see this scar. I'll see this scar every day of my life and will be reminded of this attack, no matter how hard I try to forget. I feel my happiness has been stolen from me.

“And I keep wondering: 'Why me?"

When interviewed by the police, Walker refused to cooperate. He simply slumped his head on to the table, as if asleep.

Marion Weir, for Walker, said he was ashamed and disgusted with himself. “He's tried to come to terms with what happened,” she said.

“He acknowledges that she did nothing to deserve this. He wants to deal with his issues and find out why it happened.”

Passing sentence, Judge Peter Davies praised her courage in the face of such violence.

“The photographs are a demonstration of the persistent, frenzied violence you imposed on that lady,” he said. “This was a sustained, callous, savage and brutal attack by a young man.”

What happened was part of a disturbing pattern of the defendant's past violent behaviour, fuelled by valium and cocaine.

As well as imposing the jail term, the judge ruled that Walker must remain on the Sex Offenders' Register indefinitely. The judge said Walker posed a “significant” risk of serious harm to the public – particularly women.

He will serve at least two thirds of his sentence and will only be released once the Parole Board has concluded he is safe to be out. After his sentence is expired, he must serve an extra five years on licence.

After the case, Detective Constable Jim Grattan said: “There is no excuse for Walker’s unthinkable actions and I am glad that he is now facing a significant sentence for his crimes.

“Rape and sexual offences have a huge impact on a victim and their families and I hope that today’s sentencing offers some sort of closure. She has shown true bravery throughout our investigation.”

The picture of the victim's injuries was released by police with her permission.