The parents of a woman who was robbed and sexually assaulted on Hampstead Heath stormed out of a courtroom in anger after her 16-year-old attacker was jailed for just one year.

The Hampstead youth, who cannot be named for legal reasons, violently robbed two women before groping them during late night sex attacks near Parliament Hill on August 5 and 8. During one of the incidents, he bit his victim on the groin.

A man who was hit with a claw hammer after chasing the youth for half a mile for stealing a woman’s handbag has been recommended for a police commendation.

On Friday, Judge David Richardson sentenced the teenager to two years in youth detention. In real terms, this means he will only spend one year behind bars before being released on licence.

Johanna Robinson, senior manager at sexual assault charity The Survivors Trust, questioned the length of the sentence.

She said: “Court processes are very harrowing for victims and sentencing, especially when so short. Too often, it does not reflect the impact of offences on victims and families and can even further traumatise people. I sincerely hope both victims are able to access support to help them manage the full impact of the offences committed against them.”

In the first attack on August 5, the teenager attacked a jogger as she ran on the Parliament Hill Athletics Track at night.

He pushed her to the ground before taking her iPhone 4 from her hand and touching her sexually. As he cycled past her, he threatened to orally rape her.

Three days later, the youth punched a second woman in the back of the head, knocking her to the ground. He touched her sexually and bit her on the groin before running off with a cool bag she had been carrying.

Later that day, he wrestled a handbag from another female victim but was chased for about half a mile through Hampstead by resident Louis Chang.

The teenager then produced a concealed claw hammer and hit Mr Chang, before escaping.

The court heard the teenager had a troubled past, with a previous conviction for setting fire to a pigeon at a railway station.

He had recently moved to hostel accommodation after his foster carers could no longer look after him, and struggled to cope with living semi-independently.

Mr Richardson sentenced the youth to two years for three counts of robbery and one year for the two sexual assaults, possession of an offensive weapon and causing actual bodily harm, to run concurrently.

He said: “You come from an extraordinarily troubled background and have been in foster care, no doubt for reasons related to that background but you have one previous conviction and that makes a difference. But I bear in mind your age.

“You have made progress in custody. That is a different story to the story I hear in relation to many young offenders.”

A spokesman for the Judicial Office said: “Judges sentence according to the facts and the law applying to each case and within the sentencing guidelines.”