A man told police a false "extraordinary tale" about a group of powerful figures who sexually abused and murdered boys, a court has heard.
Carl Beech, 51, is accused of lying about "three child murders, multiple rapes, kidnapping, false imprisonment and widespread sexual abuse".
His claims led to a £2m Metropolitan Police investigation, which ended with no further action being taken.
Mr Beech denies 12 counts of perverting the course of justice and one of fraud.
Mr Beech, formerly from Gloucester and known as "Nick" when he first made the claims, was in Newcastle Crown Court on Tuesday for the start of his trial.
He claimed that he was first sexually abused by his stepfather, Major Ray Beech, when he was seven years old and went on to allege abuse by a group of public figures, including from politics and the military.
Among those he accused was former Conservative prime minister Sir Edward Heath, ex-Tory home secretary Lord Brittan, former head of the armed forces Lord Bramall and former Conservative MP Harvey Proctor.
The jury was told Mr Beech picked his "targets" after browsing the internet.
Detectives investigated Mr Beech's claims until 2016 when they asked another police force - Northumbria - to investigate the accuser himself.
Northumbria Police found his story to be "totally unfounded, hopelessly compromised and irredeemably contradicted", the court heard.
Prosecutor Tony Badenoch QC told the jury: "It is quite impossible to conceive of allegations of a worse kind to be made."
He said "immeasurable distress" had been caused to those accused and those close to them - and they had suffered "obvious reputational damage".
Mr Proctor has spoken freely in public to defend himself against the allegation that "he is a sadistic child killer and that he committed other serious sexual offences", the court heard.
Jurors were told that, as an entirely innocent man, Mr Proctor was "still enraged".
Both Mr Proctor and Lord Bramall had their homes searched as a result of the allegations.
Lord Bramall's wife died during the police inquiry - codenamed Operation Midland - and Lord Brittan died while under investigation.
'Parties where abuse happened'
Mr Beech claimed the abuse happened after school, when he was picked up by a driver and taken to "parties" where there were 10 to 15 men and around seven or eight boys.
Mr Beech "claimed that he was the victim of much of the abuse and he was a direct witness to the killing of three young boys", the court was told.
Mr Beech told police that he witnessed Mr Proctor killing a boy.
Jurors heard how Mr Beech alleged that at an army location, the former head of MI5, Michael Hanley, and the former head of MI6, Maurice Oldfield, subjected him to torture.
Mr Beech claimed he had spiders tipped on him, electric shocks and darts thrown at him.
The prosecutor said Mr Beech had described to police "the most horrific sexual and physical abuse", but that his medical records did not substantiate the claims.
The court also heard that the defendant's ex-wife, whom he married in his early 20s, did not notice any marks on his body and saw nothing physical that supported his claims of electric shock treatment nor any savage abuse.
The court was played a video interview Mr Beech had given to the Met Police in November 2014, during which he cried as he described details of the first alleged murder.
He claimed a schoolmate called "Scott" was deliberately run over in Kingston-upon-Thames in 1979.
The court heard Northumbria Police concluded "there is no supporting evidence whatsoever" to support Mr Beech's account about Scott.
Prosecutor Mr Badenoch told jurors: "There was no such homicide. No missing boy."
Mr Beech also claimed that one of the boys he witnessed being murdered was Martin Allen, a 15-year-old boy who went missing in London in 1979 and has not been seen since, jurors heard.
Martin Allen's brother Kevin was contacted by Scotland Yard in 2014 and told his brother may have been linked to a VIP paedophile ring.
Mr Badenoch said: "The source of that false hope to Kevin Allen, 35 years after his brother went missing, was ultimately the false allegations of this defendant, Carl Beech."
And jurors were also told that Mr Beech had claimed he had a lifelong fear of water and could not swim, because aspects of the alleged abuse involved being held underwater and thrown in a pool.
But, the prosecutor said, police found photographs and videos of him swimming all over the world over several decades, ranging from with children at theme parks, to honeymoon snorkelling for shells, and at a pool with flippers, mask and snorkel.
It was "an adult lifetime of swimming memories", Mr Badenoch said.
'Fled to Sweden'
The court heard how the Met Police spent £2m on their investigation into Mr Beech's claims and described them publicly as "credible and true".
He first contacted Wiltshire Police in 2012 with allegations of abuse by his stepfather as well as Jimmy Savile. Between 2014 and 2016 he made further allegations to the Met Police, with a list of alleged abusers.
In 2016, when that investigation ended with no further action, police began investigating Mr Beech himself.
Police searched Mr Beech's Gloucester home in November 2016 and seized several electronic devices.
During their investigation, a number of Mr Beech's claims "were found to be provably false", the court heard.
"He had lied about the content of these allegations, taken active steps to embellish a false story, and then cover his tracks when challenged," Mr Badenoch said.
When questioned by police about this, he "fled the country and lived overseas as a fugitive" before being located in Sweden.
The jury also heard that Mr Beech's former teachers had said he had good attendance - contrary to his claims of being taken out of lessons to be abused.
The trial continues.