Craig Roy, 19, told he must serve at least 18 years for stabbing 16-year-old Jack Frew to death with a kitchen knife in May 2010

A teenager convicted of murdering a "happy, loving and vibrant" schoolboy has been given a life sentence and told he must serve a minimum of 18 years.

Jack Frew, 16, bled to death when he was stabbed 20 times with a kitchen knife. His throat was slit during the attack in secluded woodland near his school in East Kilbride, South Lanarkshire, in May 2010.

Craig Roy, 19, was sentenced at the high court in Edinburgh on Thursday. He was convicted at Glasgow high court in January, after claiming Frew had pestered him and tried to blackmail him for sex.

During the 12-day trial, the jury heard that Roy had cheated on his long-term boyfriend Christopher Hannah with Frew and was plagued by guilt over his infidelity.

He admitted stabbing the openly gay teenager but claimed to have no memory of it.

On the night of the murder, he said Frew had sent a text message telling him to meet him in woods near their school. He claimed to have taken the knife to the meeting to scare the younger boy into leaving him alone.

Frew's windpipe was cut open, his lungs were punctured and there was knife damage to his ribs.

Instead of calling an ambulance for the dying teenager, Roy phoned his boyfriend for help for himself.

It took a jury less than two hours to return a unanimous guilty verdict.

After the conviction, Frew's parents, Lorraine and Robert, said their son was "a happy, loving vibrant boy who loved life and brought fun and laughter to every situation".

They added: "Jack loved people, had the world at his fingertips with a promising future ahead and he would have made the most of every minute."

In court on Thursday, Lord Doherty described the attack as "brutal and merciless".

Sentencing Roy, he said: "You have been convicted of murder. By law, the sentence which I require to pass is one of detention without limit of time. That will be backdated to the date of your conviction.

"I also require to determine a period which represents the punishment part of that life sentence.

"At the time of the offence you were aged 17 years 10 months.

"You had no previous convictions. You armed yourself with a knife which you brought to the scene of the crime. Using it, you carried out a brutal, sustained and merciless attack which left your victim dead and mutilated.

"In the whole circumstances, the punishment part which I fix is 18 years."