Home secretary Theresa May is to launch a wide-ranging inquiry into child sex abuse claims amid fears Westminster may be facing a crisis worse than the expenses scandal which destroyed public trust in politics five years ago.
In a rapid government U-turn May will announce an inquiry into why the historic claims, which date back to the 1980s, were either missed or ignored and amid mounting suspicions of another establishment cover-up. Previously minister had ruled out such a probe.
It is understood the inquiry will cover the way several institutions, including the government, the BBC and the NHS, dealt with such abuse claims as well as dealing with the specific row over the now-famous missing dossier about the alleged paedophile ring in Westminster.
The move comes amid a flurry of fresh revelations about senior political figures allegedly involved in a number of cases.
And it follows remarks from former minister at the time of the core allegations, Lord Tebbit, that it was possible an "unconscious" cover-up may have taken place as the "system" had a tendency to protect itself.
Meanwhile politicians across the political divide have united to call for a full, Hillsborough-style inquiry to finally get to the bottom of the claims, although they are also concerned any such inquiry should not cut across the police investigations into historic abuse cases currently under way.
A number of MPs including former ministers have said they are ready to use the "nuclear option" of parliamentary privilege to name suspected paedophiles unless action is taken to properly investigate all the claims
Latest revelations include a report by the Telegraph newspaper that police have tracked down a man living in the US who claims he was assaulted by a senior politician in the 1980s when he was a child.
There have been ongoing claims that a Labour politician, who became a minister in Tony Blair's government, was part of a paedophile ring.
And it has been alleged a senior politician was found coming through customs with child pornography but no action was taken.
Most recently, the BBC has reported the former leader of the infamous Paedophile Information Exchange stored material at the Home Office when he was employed as an electrical contractor in the 1970s and 80s.
Steven Adrian Smith had clearance to work in the building when he chaired the Paedophile Information Exchange and allegedly had an office. He was jailed in 1991 and 2011.
One of the current ongoing inquiries is into whether PIE was ever given public money at that time and suspicions of a paedophile network in Whitehall.
And it has been confirmed that more than 100 documents, part of a dossier of abuse claims passed to then Home Secretary Leon Brittan in the 1980s by the late Tory MP Geoffrey Dickens, have gone missing.
Quite separately Brittan has confirmed he was interviewed by police last month over a historical allegation of rape of an 18-year-old woman in 1967.
He issued a statement confirming he was questioned but insisting: "This allegation is wholly without foundation".
He also welcomed the plans for a fresh inquiry, adding that claims he had not properly dealt with the dossier of allegations was also "completely without foundation".
"As I made clear in the statement that I issued on 2 July, I passed this bundle of papers to the relevant Home Office officials for examination, as was the normal and correct practice," he said.
But there are real fears that the inquiry may further damage the reputation of politicians way beyond the expenses scandal, particularly if it discovers evidence of current abuse claims.