No police were stationed inside the 2017 V Festival in Essex because of a dispute over money, the BBC's Victoria Derbyshire programme understands.
The organisers, Festival Republic, refused to pay the cost of special police services at the 50,000-strong event, Chelmsford City Council documents show.
There were also concerns over the vetting of staff and drug dealing.
Festival Republic has not responded to a request for comment.
Essex Police said policing for a private event was the duty of organisers and not compulsory and it had had armed officers patrolling outside the festival's cordons.
Power to arrest
Meeting notes from Chelmsford City Council's Safety Advisory Group (SAG) – obtained by the Victoria Derbyshire programme by Freedom of Information request – suggest that in 2016 Festival Republic spent £138,000 on special police services.
In 2017, organisers submitted a request for police services at a cost of £100,000, but an agreement on the level of policing and money could not be reached.
As a result, no police officers were stationed on site.
The festival took place two months after 22 people were killed in a terror attack during a concert at Manchester Arena.
Security officials used by the festival did not have the power to arrest or detain individuals, and were advised to dial 999 for emergencies and 101 for non-emergencies.
SAG meeting notes show in October 2017, a council representative highlighted "that reporting to the police via the 101 number was an issue" as there was no dedicated support to festivalgoers, and that "drugs were the biggest concern, with no police presence on site".
The alleged sexual assault of a 13-year-old girl was reported to Essex Police, but by the time officers reached the site they were unable to find the suspect's tent, in which the alleged assault was said to have taken place.
A suspect package was also found on site during the festival, documents suggest.
'Far too late'
Meeting notes suggest Essex Police were unhappy that the vetting of some 740 staff working on site was "left far too late" and that "some vetting was still going on when staff were on site, by which point it is too late".
A Chelmsford City Council representative also stipulated that "last minute arrangements for this year's festival were unacceptable and this must be improved upon from now on".
"The 2018 event must be planned well in advance, and an agreement in principle can be made before tickets sales are known," the representative added.
Deputy Chief Constable BJ Harrington said: "I really must stress that the safety of a commercial event like V Festival sits with the organisers.
"They are licensed by the local authority, and that safety of people attending their event on payment is down to them.
"That doesn't mean we abandon them. We had a really good working relationship with security, with Chelmsford City Council, to make sure that people who were going there were safe."
The council meeting notes also suggest Essex Police did not believe its tactical plan for security at the event had been met by the Safety Advisory Group and festival organisers.
Chelmsford County Council said: "The Safety Advisory Group process allows a transparent and robust examination of all safety issues prior to and during the festival to ensure any risk to safety is properly managed and mitigated.
"The lack of agreement on special police services was a risk which the festival promoter resolved through alternative means to the satisfaction of the Safety Advisory Group."
Watch the BBC's Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News channel.
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