Police paid a convicted child rapist almost £10,000 to spy on parties where they believed underage girls would be sexually abused, a court has heard.

A total of 17 men and one woman have been convicted of, or have admitted, charges that range from rape to inciting prostitution and supplying drugs, in a series of trials at Newcastle Crown Court.

During the trials, it was heard that Northumbria Police recruited a sex offender years after he drugged an underage girl and invited another man to rape her after he had done so.

The convict, who can only be named as XY, was tasked to assist the force with its investigation into child sexual exploitation in Newcastle.

Defending his force's use of an informant, Northumbria police chief constable Steve Ashman said he would "not rule out" using a convicted rapist to aid an investigation again.

He said "we have safeguarded vulnerable women and girls" and "dangerous men are behind bars" because of the information gathered using the convicted rapist.

Mr Ashman said: "We have to step into a murky, dangerous and shadowy world and the people who are going to provide us with that information which will protect victims - it's not the post-master or the district nurse."

He went on to say: "We were absolutely entitled to do what we did. The question that remains is a moral one: was it right to do that?"

Subsequent trials, which until now were unreportable, have heard girls were groomed by men who gave them cannabis, alcohol and the designer drug Mkat at parties, then encouraged them into having sex.

Police said they found 278 victims and over the course of four trials 20 young women gave evidence.

Those prosecuted were from the Bangladeshi, Pakistani, Indian, Iraqi, Iranian and Turkish communities and mainly British-born, with most living in the west end of Newcastle.

During pre-trial hearings, defence barristers argued the cases of more than 10 men should be thrown out due to the informant's involvement.

Robin Patton, representing one of the defendants, said the public's confidence in the justice system would be "substantially diminished" if they knew police had recruited "such an individual".

David Hislop QC, representing another defendant, said XY had 13 previous convictions, including 26 offences of dishonesty.

:: Snouts and narks: The murky world of police informants

It was heard that after his recruitment, the informant was arrested after a teenage girl claimed a man approached her and made an indecent proposition.

He was later told he would face no action after he took part in an identity parade.

During legal submissions, XY gave evidence to the court and made a series of lurid allegations against the police, including claims of racism and that he was asked to plant drugs.

He claimed he was recruited because he acted as an informal taxi driver for some of the defendants and "had to make it look like I was their friend".

Judge Penny Moreland rejected his evidence in its entirety, describing it as "inherently unreliable" and "clearly dishonest".

Former undercover police officer Neil Woods, who used to recruit and pay police informants, described the method as the "cheapest and most efficient way of solving crime".

He went on to say that "the vast majority of informants are used for drug offences", but only for robberies or sex crimes "in rare cases".

Former detective chief inspector Chris Phillips, told Sky News: "No officer would ever go into work thinking they were going to pay a convicted rapist money, but sometimes the needs are to get a prosecution, and you will only get that with enough information to put before a court.

"Countless lives have been saved by the use of informants, and if we have to pay £10,000 to get these people's locked up, I think it's money well spent."

In a statement, the NSPCC said it was "appalled" Northumbria Police recruited a convicted child rapist as an informant.

"It beggars belief that it would ever have been considered, let alone approved, and serious questions must be asked about the force's approach to child sexual exploitation operations," it said.

"However good the force's intentions, their misguided actions run entirely counter to all current child protection procedures and what we know about sex offenders and could have compromised this investigation."