He was finally tracked down in Tenerife with help from the Catholic Church

In August last year, he was detained under a European arrest warrant and extradited to the UK.

Yesterday, he pleaded guilty to 21 charges of abuse against children as young as six, including altar boys, between the 1950s and 1990s.

But the case has prompted questions over who withdrew the arrest warrant and how he was allowed to go on the run for so long.

Detectives say they stopped looking for Father Cullen when the warrant was withdrawn and the Crown Prosecution Service says it had nothing to do with the move.

But a spokesman for the Ministry of Justice said the court that Cullen failed to attend – Nottingham Magistrates' – should hold a record of who asked for the application for the warrant to be cancelled. A clerk there said all relevant documents had been passed to Derbyshire Police.

Chris Leslie, MP for Nottingham East, said: "There are clear issues that have arisen here and I think it's important the procedures are revisited, questioned and accounted for.

"This is a shocking saga and clearly there have been many victims scarred by this evil behaviour. It is the sort of case that will cast a long shadow over the whole community."

Derbyshire Police became involved in the investigation when another victim came forward in 2005, and a new warrant was issued for Cullen's arrest.

Shuffling into the dock at Derby Crown Court yesterday, Father Cullen looked gaunt as he admitted 15 counts of indecent assault, five of indecency with a child and a further sexual offence.

The offences took place between 1957, when Cullen was 28, and 1991.

Judge Jonathan Gosling adjourned sentencing until March 24, warning the paedophile that he faced "a lengthy prison sentence".

He was remanded in custody.

The court was told how officers from Derbyshire police approached the Catholic Church in Nottingham to see if it could help track Cullen down and the church's safeguarding team traced him to Tenerife, where he was attending church.

Father Andrew Cole, spokesman for the Catholic Diocese of Nottingham, said: "We are very pleased he has admitted what he has done. He has pleaded guilty, meaning those who he committed these abhorrent crimes against will not have to face him in court."

Father Cole said the Catholic Church took the safeguarding of children and vulnerable adults "extremely seriously".

Yesterday, as news emerged of Cullen's guilty pleas, parents in Hyson Green reacted with horror.

Mum Sarah Leavers, of Hyson Green, was in a rush to collect her daughter from nearby St Mary's Primary School. She said of Cullen's crimes: "He wants hanging. It's disgusting."

Adrian Kinch, 46, who works in Hyson Green, said: "I'm glad Cullen has now been caught. Obviously, it's the children who have suffered not him."

A woman who would only give her first name as Olivia was cleaning the church railings. She did not know Cullen but said: "We pray for the children and the families who were abused. It's terrible."

In court yesterday, the charges were put to Cullen. Softly spoken, he bowed his head and replied "guilty" to each one.

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Francis Paul Cullen must have had more victims, a court heard.

The priest, who spent three years working at St Mary's Catholic Church, in Hyson Green, yesterday pleaded guilty to 21 charges of abuse against children as young as six, including altar boys, between the 1950s and 1990s.

But investigating officer Detective Constable Matt Goodwin said it was "inconceivable" that Cullen, who is now 85, had not abused more children during his time as a priest.

He said police would investigate any new allegations made if anyone chose to come forward.

The Nottingham Catholic Diocese, which covers Derbyshire, said there were no records of reports being made to the diocese at the time of the abuse.

Father Andrew Cole said: "There is absolutely no evidence whatsoever that anybody complained to the Church."

But one victim said he believed his parents did report the abuse to the church.

Cullen was first charged with sexual abuse against three boys in Nottinghamshire in 1991 but did not turn up to court and an arrest warrant was issued against him.

However, he was not arrested until more than 20 years later, when Derbyshire police, investigating new allegations against him, tracked him down in Tenerife.

In August last year, he was detained under a European arrest warrant and extradited to the UK.

He was charged with offences against one of the three alleged victims in 1991 and two other people, who had been abused as boys in Mackworth, Derby, and had come forward after Cullen went on the run.

Four more victims came forward following publicity about his extradition, and he was also charged with those offences.

DC Goodwin said: "These convictions show abhorrent behaviour by this former Catholic priest. He was in a position of trust and his role gave him access to these young and vulnerable children, who he went on to abuse."

Cullen used his position in the church to intimidate his victims, the court was told, and carried out the sexual abuse on church and school premises as well as in his home, a caravan and a hotel.

Cullen's abuse had had "a significant impact" on his victims and some who were abused repeatedly had been deeply traumatised by the experience, said DC Goodwin.

"His main weapon of control was the fact he was a Catholic priest and the power of his position over those in that faith is what kept them quiet.

"A recurring theme is whenever a victim realised what was happening was wrong and started to withdraw or go to church less, then the abuse would stop."

The first recorded complaint made to Derbyshire police was in 2005 by a man who said he was abused by Cullen between the ages of eight and 16 in the 1960s, when Cullen was based in Mackworth.

The allegations were investigated but Cullen could not be traced.

In 2006, a woman told police she had been abused by Cullen from the age of six to 12 in the 1980s, when Cullen was at Buxton.

Over the following years, the case was opened and closed three times as new evidence came to light but Cullen could still not be found.

Then in 2011, DC Goodwin became involved in the investigation and his inquiries led to the discovery of Cullen's whereabouts.

In 2012, Nottingham Catholic Diocese safeguarding office contacted the officer and told him Cullen had been in Tenerife for 20 years and regularly attended Mass there. Inquiries to Interpol had also confirmed that Cullen had links with Tenerife. Also at this time, another victim came forward – he had been abused by Cullen between the ages of seven and 14, starting in the 1950s.

Derbyshire police applied for Cullen to be extradited to the UK and he was arrested by the National Crime Agency on August 20 last year. He was charged with abusing three boys – the one who came forward in 2005, the one who reported it in 2012 and one of the boys from Nottingham, who Cullen had been charged with assaulting in 1991.

One of the three victims from Nottingham could not be traced and the Crown Prosecution Service decided there was not enough evidence to charge Cullen with offences against another victim.

Following publicity over his arrest, three new victims came forward as well as the woman who had reported it in 2006.

The new victims included a woman who was sexually assaulted by Cullen when she was 13. "He was left alone with her and sexually assaulted her," said DC Goodwin.

The others were two men who had been sexually assaulted by Cullen when he was based at Mackworth in the 1960s – one repeatedly between the ages of six and 12 and the other on one occasion when he was 11.

Cullen was charged with offences against these other four victims earlier this month.

One victim said he had told his parents about the sexual assault and they had reported it to the church.

"As far as this victim is concerned, a man from the church, who was higher up than Francis Cullen, came to his house," said DC Goodwin.

"He was sent from the room and believes the conversation was about the assault. As far as he is concerned, the allegation was not taken any further."