Darkness, rain and a lack of officers stopped police from closing down an illegal rave which attracted up to 2,000 people to a beauty spot.
Officers were called to Devils Dyke, five miles north of Brighton, at 1am on Sunday but did not stop the party because poor weather conditions, the volume of people and the number of officers available meant "it was not appropriate or practical to attempt to close the gathering safely", according to Sussex Police.
More than 24 hours after complaints were made about the noise and the "serious distress" the rave was causing people living in the nearby village of Poynings and the hamlet of Saddlescombe, the party came to an end during the early hours of this morning, police said.
At its height, 400 vehicles, seven sound systems and an estimated 2,000 people were present, but rather than stop the rave on the land, which forms part of Sussex's South Downs, police set up road blocks to prevent further people from turning up.
Linda Freedman, chairwoman of Brighton and Hove Conservatives, told the Argus newspaper she walked up to the rave and saw people "out of their heads".
When she asked a nearby officer what the police were planning to do about the situation, she was told: "We only have four officers, so there's nothing we can do".
A Sussex Police spokesman said there had been a noticeable decrease in party-goers from midnight and by 7am just one car, which had broken down, remained at the scene.
He said seven arrests were made: five for drugs offences, one for driving while unfit through drugs and one for failing to comply with a direction to leave the area, but that there were no reports of disorder or injury.
Breath tests were also carried out on drivers leaving the beauty spot but no-one was arrested.
He said: "About 90% of the rubbish had been collected into bags and left at the site by those leaving, assisting collection by the landowner.
"During Sunday, police had set up road blocks to help prevent further people arriving and we believe this, together with social media messaging drawing attention to the road blocks, had an impact on numbers and on the event winding down earlier than might otherwise have been the case."
He said officers had reassured residents action was being taken to minimise the impact on them and that police were looking into the organisation of the rave to see if any offences had been committed.
He continued: "Officers were on the site during the day and the gathering was good-humoured but very noisy.
"Although there are powers available to the police to close down illegal gatherings such as this, before exercising these powers an assessment has to be undertaken to determine whether or not such a gathering can be closed down safely and effectively.
"The assessment was that it would not be possible or safe to close the event down, given the number of police officers available, but a police presence at the location was maintained and active measures were taken to seek to prevent it escalating further."
Chief Superintendent Wayne Jones said: "These raves can cause a huge amount of disruption to local residents and damage to the land.
"Where we can, we will attend a report at the earliest opportunity to try to bring it to a safe conclusion.
"When a large number of people are already at the site it is not always possible for us to shut down the rave safely with the police resources available at that time.
"However we will always take action to contain the event, to reassure local residents, and work with partners, such as the National Trust in this case, to minimise the impact."