LONDON—Britain’s political and legal institutions covered up serious allegations of child sex abuse by turning a blind eye to evidence of pedophile attacks and protecting serial abusers who were part of the political establishment, according to an inquiry report published Tuesday.

Margaret Thatcher promoted a top aide and knighted him despite knowledge within the Conservative party that Sir Peter Morrison was an active and dangerous pedophile. The Liberal and Green parties were also accused of failing to deal with pedophiles in their own ranks.

The report by the Independent Inquiry into Child Sexual Abuse concluded that members of London’s political elite valued the maintenance of their reputations more highly than the fate of children who were exposed to serial offenders. They found failings that stretched more than half a century from the 1960s up until 2017.

“It is clear to see that Westminster institutions have repeatedly failed to deal with allegations of child sexual abuse, from turning a blind eye to actively shielding abusers,” said the chair of the inquiry, Prof. Alexis Jay. “A consistent pattern emerged of failures to put the welfare of children above political status.”

The inquiry, which was established in 2015, found that there was a culture of deference within law-enforcement agencies who were unwilling to challenge senior politicians.

The Conservative lawmaker, Victor Montagu, the 10th Earl of Sandwich, was allowed to escape with a caution when a 10-year-old boy accused him of indecent assault. Montagu’s son Robert told the inquiry that he had also been sexually abused by his father and he was appalled by the attitude of the British justice system. Montagu was a member of parliament (MP) until 1962. “[The decision not to prosecute was] entirely wrong and very indicative of the attitude towards people in public positions,” he said.

The report found that there was “ample evidence that individual perpetrators of child sexual abuse have been linked to Westminster” but it found there was no evidence to support Scotland Yard claims in 2014 that there was an organized network of abusers who passed victims around between them.

The inquiry found: “Several highly placed people in the 1970s and 1980s, including Sir Peter Morrison MP and Sir Cyril Smith MP, were known or rumoured to be active in their sexual interest in children and were protected from prosecution in a number of ways, including by the police, the Director of Public Prosecutions and political parties. At that time, nobody seemed to care about the fate of the children involved, with status and political concerns overriding all else.”

Smith, the Liberal MP for Rochdale from 1972 to 1992, admitted abusing boys at a hostel in the 1960s when he was a local politician but was never prosecuted by the authorities or sanctioned by his party. David Steel, who now sits in the House of Lords, was leader of the Liberals between 1976 and 1988. He told the inquiry that he had found out about the pedophile attacks but saw “no reason, or no locus to go back to something that had happened during his time as councillor.”

The report concluded that: “This failure to recognise the risk that Cyril Smith potentially posed to children was an abdication of responsibility by a political leader and an example of a highly placed politician turning a blind eye to something that was potentially troublesome to his party, with no apparent regard for criminal acts which might have occurred or for any victims, past or future.”

Hours after the report was published, Steel announced that he would reluctantly stand down from the House of Lords and the Liberal Democrats.