LONDON — A toxic mix of misuse of power and official silence has become Britain's shame as the country faces up to a growing web of evidence that the abuse of vulnerable children by powerful men was covered up for decades.

Several lawmakers said Tuesday that former detectives and intelligence officers should be guaranteed protection from prosecution if they speak out about child abuse by senior police, politicians other prominent people.

On Monday, the BBC's "Newsnight" program reported that an ex-detective had told it that a lawmaker, Cyril Smith, was arrested in the early 1980s as part of an investigation into child-sex parties, but was released hours later.

He said officers were ordered to hand over notebooks and video footage from their undercover operation, and were told they would be violating the Official Secrets Act if they revealed what had happened.

The BBC did not identify the former detective because of the legal threat hanging over him.

After Smith died in 2010, prosecutors revealed that in 1970 eight men had accused the Liberal lawmaker of abusing them as teens. The prosecutors said Smith was never charged, but should have been.

Deputy Prime Minister Nick Clegg said Tuesday that the BBC was alleging "very, very serious dereliction of duty and of wrongdoing" against police investigating "some of the most grotesque crimes imaginable."

"I would just very much hope the police now can investigate this very thoroughly without fear or favor, get to the bottom of the truth," he said.

A dam of official silence around child abuse in Britain began to break after the 2011 death of entertainer Jimmy Savile, who was exposed as a predatory pedophile who assaulted victims in hospitals, children's homes and TV studios over several decades.

Since then, several once-prominent entertainers have been convicted and police have reopened dormant abuse inquiries.

But police themselves are accused of having been part of the problem. On Monday Britain's independent police watchdog said it was looking into allegations that Scotland Yard covered up historic allegations of child abuse from the 1970s to the 2000s.

Labour Party lawmaker Tom Watson, who has campaigned to expose sexual abuse by politicians, said former police officers and civil servants with information should be protected from prosecution if they speak up.

He said it is "the duty of all former police officers, intelligence officers and civil servants who have knowledge of a cover-up to come forward."

The British government has ordered a public inquiry into how public agencies — including government bodies, police, hospitals, churches and the BBC — handled child-abuse allegations.

The abuse claims reach so deeply into the upper echelons of British society that finding a figure to head the inquiry has been problematic. Two chairwomen were appointed and then rejected because of their connections to the Establishment. Last month a judge from New Zealand, Lowell Godard, was selected to lead the probe.