The calls for an inquiry into allegations of a cover up of a paedophile ring that might have included senior politicians in the 1980s are growing louder. The disappearance, revealed in this weekend's Observer, of not one but 114 files relating to possible child sex abuse has added weight to the case originally raised by two MPs, Tom Watson – who a year ago revealed the existence of a file of charges put together by the late Conservative MP Geoffrey Dickens – and the Rochdale MP Simon Danczuk, the man who outed his predecessor in Rochdale, Sir Cyril Smith, as a child abuser. Mr Danczuk told the BBC that he was now so confident of his information that he was ready to name at least one MP, although only under the parliamentary privilege that would protect him from legal action. Then on the Andrew Marr showon Sunday, Lord Tebbit, who was both party chairman and a cabinet minister in the era in question, admitted that he thought it was "likely" there had been an "enormous" cover up. As he said, in those days protecting the system came before hunting down wrongdoing.

Public inquiries can do three things. They can act as a catharsis for people who have suffered harmed; they can uncover the existence of systemic or institutional failure; and they can learn lessons. Some inquiries have been exceptionally important in fulfilling the first of those objectives – Sir Ian Kennedy's into the child deaths at Bristol Royal infirmary, for example. The inquiry into the murder of Stephen Lawrence, with its devastating conclusion of the existence of institutional racism in the Metropolitan police, was a good example of the second. And Lord Laming's painstaking investigation into the death of Victoria Climbié, which transformed social work practices relating to child protection, fulfilled the third. The question now, in the fevered atmosphere of mid-summer Westminster, is whether there is a case for an inquiry into these latest allegations of the secret existence of a high-level paedophile ring.

There are two separate aspects of this current storm. One is the fate of the victims, of whom so far nothing at all is publicly known. That may, of course, be because there are none. Westminster is well rehearsed in the matter of spinning complex webs of conspiracy on too few facts. It is always possible that this case is the product of well-meaning but overheated imaginations. But there is so much evidence from the continuing cases of historic sex abuse that shows how shame, humiliation and fear of being disbelieved deter victims from coming forward – the TV personality Vanessa Feltz is merely the latest to reveal that she failed to make a formal complaint against Rolf Harris – that if there were a real scandal, its victims would be deeply traumatised individuals who may well still lack the confidence to come forward.

The second is Westminster and Whitehall's ancient practice of protecting its own, of which the expenses scandal may have been the most egregious example, that has led to such a damaging collapse in public confidence in politics and parliament. In this context, the Home Office promise of a review of the review triggered when Tom Watson first raised the Dickens allegations a year ago is insufficient, although the decision to appoint an external investigator with a judicial background is a small advance. However, as the shadow home secretary Yvette Cooper has demanded in a letter to Theresa May, it needs to look much further. It must try to establish the contents of the disappeared files and what action if any they triggered, with what result. If these allegations are found to be true, then it will confirm again the terrible extent of the failure of child protection – and it will be more important than ever to be confident that the reasons for it are properly understood.

It is now obvious that the scale of child sex abuse has been greater and has gone on for longer than many people might have imagined. So the question that most urgently needs answering is who knew, and why didn't they act.