The Chief Executive of Oxfordshire County Council has insisted she will not be resigning after seven members of a paedophile ring were found guilty of child rape, trafficking and organising prostitution in Oxford.

Joanna Simons said that although the council “take enormous responsibility for what's happened”, her “gut feeling” is that she will not resign.

Ms Simons said the council would be asking itself some “very hard questions” in the wake of the case, which involved girls as young as 11 being drugged and raped by members of one of Britain's biggest ever child sex gangs.

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The crimes took place over eight years and social services and the police have apologised for not acting sooner.

Ms Simons, who has been the council's chief executive since 2005, added: “There is going to be an independent serious case review which will look at the actions of all the agencies concerned... [but] my gut feeling is that I'm not going to resign because my determination is that we need to do all that we can to take action to stamp this out.”

She went on: “These are devious crimes that are very complicated.”

Child protection experts said that the six victims of the ring were “let down by those who were meant to care for them and obvious signs of abuse were missed”.

The fact that the gang was able to continue its brutal sexual abuse despite the concerns of social workers and reports to police officers at a relatively early stage will now be the subject of an independent investigation.

The seven men, aged between 27 and 38, were warned to expect long jail terms for the gang's eight years of offending involving vulnerable young girls in Oxford. Judge Peter Rook told them: “You have been convicted of the most serious of offences. Long custodial sentences are inevitable.”

Two sets of brothers, Akhtar Dogar, 32, and Anjum Dogar, 31, and Mohammed Karrar, 38, and Bassam Karrar, 33, were convicted of sex crimes, along with Kamar Jamil, 27, Assad Hussain, 32, and Zeeshan Ahmed, 27.

Fighting broke out in the dock at the Old Bailey as Zeeshan Ahmed punched Mohammed Hussain, who was cleared of all charges. Another man, who cannot be named for legal reasons, was also cleared.

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A Serious Case Review panel headed by leading child protection barrister David Spicer will look into the failure to stop the gang, which first appeared on Thames Valley Police's radar in early 2006 when one of the victims told officers she was being held against her will.

That report was later added to by others, but police did not arrest the gang members until early 2012.Oxfordshire County Council's failure to protect the girls will also be investigated.

Many of the victims – who can only be referred to as Girls A through to F for legal reasons – were living in care homes in the Oxford area while they were being groomed and sexually abused by the gang and other men.

Both of the Dogar brothers, as well as Bassam Karrar, were arrested between August and November 2006. But all were later released and were able to continue offending for six years after the cases against them were dropped because the girls were unable or unwilling to give evidence.

Some of the victims in this case were also being abused simultaneously by other men, four of whom were subsequently charged. Two of the cases collapsed but Armit Singh, 32, and Ricky Krong, 39, were jailed for sexual activity with children. Yet despite those four cases clearly indicating that the victims were at risk of child sex exploitation, the chance to end their ordeal was again missed.

The first known case of grooming by the gang started in 2004 and took two years to come to the police's attention. In February 2006, officers spoke to Girl A, who said she had been held against her will by two Asian men. She said they "made her snort cocaine and left her unconscious".

In August that year, police were called by Girl B after she was raped. She told officers who arrived at the house she was in – along with 11 men – that she was still a teenager and had run away from a children's home. But she did not tell them of any sexual contact with any of the men and later refused to go any further with her complaint.

In September 2006, police began investigating Girl A's case. She was found in the company of one of the gang, who was interviewed over allegations of raping her. But, having denied the claims, he was allowed to walk free and would continue his abuse of her and other girls for more than five years.

Police were also to come into repeated contact with the men during 2006 – on at least one occasion while they were in the company of some of the victims. In November of that year, Girl C contacted police after being repeatedly raped, beaten and abused by Bassam Karrar. She made a complaint, but later withdrew it.

During the four-month trial, the jury heard that one of the girls in care went missing 126 times and it was the "general consensus" among staff at her home that she was being sexually groomed. They saw her being picked up from the home where she was living in 2007 and 2008 by older men and passed on their concerns to police. But it was not until February 2011 that Thames Valley Police and Oxfordshire County Council recognised that the city had a problem with the sexual abuse of children – and not until May that year that an investigation was opened. It would be 10 months before the gang could be arrested.

Thames Valley Police admitted that they were too reliant on the girls themselves coming forward. "These young women were put through a terrible ordeal. The nature of this abuse is that children were deliberately groomed, making it harder for them to resist abuse and hard for them to report it. Thames Valley Police and Oxfordshire County Council Social Services deeply regret that this wasn't identified sooner," said Detective Chief Superintendent Rob Mason.

Two of the children's homes in the area where the victims were living have since been closed down. The systems in place to protect children from harm and help them stay safe at one of the homes where some of the girls stayed was found to be "inadequate" at three successive Ofsted inspections in the year to May 2008.

In their May 2008 report, inspectors wrote: "There is a lack of a coherent strategy to discourage absconding behaviour… There is not a proactive approach to making the environment a safe and secure place for young people." On one occasion, Girls A and B had returned to their home in a taxi, but Girl B was not able to persuade staff to pay the fare, so the driver took Girl A back to Oxford where she was abused and raped again the next day.

Jon Brown, the NSPCC's head of sexual abuse programmes, said: "The Oxford grooming trial has been a grim reminder that even though we are living in the 21st century, some people have retained medieval attitudes towards young girls. The barbaric treatment in this case was depraved, almost beyond imagination and must never be allowed to happen again."

Deputy Children's Commissioner Sue Berelowitz called for health professionals and care workers to discard the normal rules on confidentiality to help protect children at risk of exploitation. She said that if doctors or social workers come across clear evidence of child exploitation they should be compelled to contact the police automatically.

The arrests that were finally made came after police began fully to understand the nature of the crime. Officers began to forge closer relationships with the victims and with social services and other agencies to uncover and disrupt the abuse.

Former Acting Detective Chief Inspector Simon Morton said: "These men were predators, by the time they had finished, they had eroded the victims' will and owned them."

He said the victims have gone through their court ordeal "to protect other girls and stop them going through what they had to go through.

"We have had to tread very, very carefully with the victims. You cannot build a relationship in a night, it takes months and months," said Morton.

"It has been really difficult for them. They have lived through it twice – personally and in open court. But they are really proud to be able to tell their story at last."

Oxford gang: Timeline

2004: Earliest case of possible grooming recorded.

February 2006: Girl A tells police she was held against her will by two Asian men, who made her snort cocaine and left her unconscious.

21 August: Girl B calls police after being raped. She tells them she had run away from a children’s home.

September: Police investigate Girl A’s case. Arrests were made but no convictions could be obtained as she refused to continue cooperating.

5 September: Police officer stops and checks Akhtar Dogar while in Girl A’s company.

13 September: Akhtar Dogar interviewed by police. Admits knowing Girl A but denies raping her.

October 2007: Social worker answers Girl D’s phone and threats are made by “Mo”. Girl D tells him Mo “takes her to houses”.

30 January 2008: Girl D meets police and welfare officers and says she has been raped by “Mo”.

22 March 2012: Defendants arrested.