An 11-year-old boy has become Britain's youngest rapist after pleading guilty to sexually assaulting a nine-year-old boy multiple times.

The boy from the North Shore area of Blackpool was discovered raping the nine-year-old after the victim's mother heard suspicious sounds over a baby monitor in his bedroom in May.

The victim told specialist police officers that the defendant had raped him nearly every time they had played together and he had told him to keep the incidents secret, the Daily Mail reports.

It is understood the nine-year-old was raped 15 times by the defendant, who is now aged 12.

Further enquires revealed the defendant had sexually touched a seven-year-old boy over his clothing and while on bail he had also sexually touched an 11-year-old disabled boy over his trousers.

The court heard the offences took place between April 2015 and August 2016.

The boy, who cannot be named for legal reasons, pleaded guilty at Blackpool Magistrate Court to one charge of raping the same boy 15 times and three charges of sexual touching, the Sun reports.

Brett Chappel, defending, said the boy had been a victim of sexual abuse himself, had pleaded guilty immediately and shown a sense of shame and remorse over the incidents.

He added that the defendant recognised he needed help for his problems and would address them.

Kerry Grieve, prosecuting, said: "He has been assessed as at a high risk of joining in further sexual behaviour."