A father has told of how his son cut off his own penis and stabbed his mother after smoking skunk cannabis.

His son became "paranoid" and took to sleeping with a tennis racquet "because he thought people were living in the walls" after taking the drug over a period of time, the unidentified man told BBC's Radio Five Live.

Skunk cannabis is a highly potent form of the drug and, according to research from 2015, can cause "significant" brain damage.

Its use can lead to an increased risk of mental illness and psychotic symptoms.

Remembering the "absolutely devastating" day his son — whose age has not been revealed — chopped off his own penis is "almost as if I'm peering in through a window and it's happening to somebody else", the man told the station.

"He switched from a very bright bubbly lad to, I can only describe it as a waste of space," he added. "I've had that conversation with him and he understands that." He first tried the drug out of "boredom", he said.