Tom Watson put pressure on Metropolitan Police officers who had an "unwarranted and disproportionate" belief in the fantasist behind claims of a VIP paedophile ring, a damning report has found.
Former High Court judge Sir Richard Henriques carried out a review of Operation Midland, the disastrous £2.5m investigation into Carl Beech's allegations which ended after 16 months without a single arrest.
Beech, who was known as "Nick" before his identity was revealed, was jailed for 18 years in July after being found guilty of 12 counts of perverting the course of justice and one of fraud.
In a 391-page report published on Friday, Sir Richard said the main cause of Operation Midland's failure was the Met Police's "poor judgement and a failure to accurately evaluate known facts," while a "major contributing factor was the culture that 'victims' must be believed".
He also said "there can be no doubt" that Mr Watson, Labour's deputy leader, "believed 'Nick'" and created "further pressure" upon Met Police officers.
In response, Mr Watson – who had raised the issue of an alleged VIP paedophile ring in parliament – said Sir Richard's review contained "multiple inaccuracies" about him.
Sir Richard accused officers of misleading a judge into granting warrants to search the homes of those wrongly accused of rape and torture by Beech.
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He found that warrants to search the properties of D-Day veteran Lord Bramall, the widow of former home secretary Leon Brittan and former Tory MP Harvey Proctor were "obtained unlawfully".
Sir Richard said: "Whilst the responsible officers assert that they kept an open mind, several failures can only be explained by an unwarranted and disproportionate belief in 'Nick's' credibility."
Sir Richard added that "the most significant error in this investigation was the decision to apply for search warrants coupled with formulating inaccurate statements which were placed before the district judge".
"But for that decision, this investigation may well have been completed without the dreadful adverse consequences I have described," he said.
Sir Richard voiced concerns that five "experienced and highly regarded" officers had expressed the view that Beech had been consistent "when he was so demonstrably not so".
He said one possibility was that the officers had not "read or sufficiently" read Beech's previous interviews with Wiltshire Police as they sought search warrants.
Sir Richard added: "As matters stand I have no doubt that the district judge was misled, and, had he known the true position, he would not have granted the applications.
"The gravity of a judge being misled in such circumstances cannot be overstated."
Five officers were referred to the Independent Office for Police Conduct but the watchdog found no evidence of wrongdoing or criminality.
Sky's crime correspondent Martin Brunt said it was "dark day for Scotland Yard" following the release of the "damning" report.
The officer in charge of Operation Midland, Steve Rodhouse, apologised for the "distress" caused, saying the report shows there are "clearly lessons to be learned for future investigations".
Meanwhile, the Met's deputy commissioner Sir Stephen House acknowledged "mistakes were made in Operation Midland" but added: "We do not agree with everything Sir Richard wrote in his report or indeed all of his recent statements regarding further investigations into the actions of officers."