A letter received by Scotland Yard in 1998 claiming the DJ was a paedophile was classed as "sensitive", meaning other investigators could not find it, Her Majesty's Inspectorate of Constabulary found.
"The 1998 MPS anonymous letter was marked as 'sensitive' because of Savile's celebrity status and because there were allegations of blackmail and paedophilia. This categorisation meant that the intelligence was not readily available to be searched by later investigating officers," the inspectors said.
Scotland Yard sent the letter to West Yorkshire Police, the area where Savile lived, but other investigators could not access the information until 2011.
The letter said:
"The image that Jimmy Savile has tried to portray over the years is someone who is deeply concerned with his fellow man; however, the thrust of this is entirely the opposite. His fundraising activities are not out of altruistic motives, but purely for selfish advancement and an easy living.
"He has slimed his way in wherever possible. He has tried to hide his homosexuality which in any event is an open secret with those who know; but did you know that he is also a deeply committed paedophile and involved in b****ry with young children.
"What can not be acceptable and must be stopped is Jimmy Savile's paedophilia. I know he has pornography, but do not know which of his houses it is in.
"Regularly, he runs for the Life charity in Roundhay Park in Leeds, he would say 'Now I've had a run, I feel like some bum'. And would then later in the evening go where the rent boys hang out.
"Please, do not let him get away with this perversion and that he feels immune because of the people he mixes with. There are too many of his perverted type around.
"Don't let him continue to think he is untouchable, or that his secret is too well hidden.
"When Jimmy Savile fails, and sooner or later he will, a lot of well-known personalities and past politicians are going to fall with him.
"I have done my duty, my conscience is clear, you have the power, time, and resources at Scotland Yard to wheedle him out, and expose him for what he really is.
"If you think this is a hoax, or a crank letter, think again. It is not I who suffer if you do nothing, but the children."
In 2007, Surrey Police investigated three complaints made against Savile, later tied in with an allegation made to officers in Sussex.
HMIC found that had Surrey known about the 1998 letter and a complaint against Savile received by Scotland Yard in 2003, the investigation would have been pursued more vigorously.
It said: "We are confident that if the Surrey investigating officers had been made aware of this material, the investigation would have been scaled up accordingly."
The HMIC report also found that Savile's celebrity status impeded investigations.
"It is absolutely clear to us as a result of this review that one of the reasons why allegations were not made at the time, or investigations were not conducted as they might have been, centres on Savile's status," it said.
"He was a well-known national celebrity, praised for his substantial fundraising efforts, and a household name to many. That fact alone allowed him access to institutions in a way that those without celebrity status would have been denied.
"We wonder, as a result, whether those responsible for investigating potential criminal offences had a different approach to dealing with allegations against those in the public eye.
"There might well have been the thought that, in order to charge a man such as Savile, there had to be that extra piece of evidence; that piece of evidence that had to be conclusive; that second or third witness to the crime - just to be sure that bringing proceedings against him was justified."
It said that officers in Sussex had Savile's status in mind when they carried out interviews, and that the victim was told it would be difficult for a prosecution to take place against "a big celebrity".