Theresa May has admitted there “might have been” a cover-up at Home Office in the 1980s concerning allegations that politicians were involved in child sex abuse but said an official review found the claim was “not proven”.

The Wanless report concluded that “shambolic” record keeping at the Home Office meant a definite answer could not be given either way. More than 100 files concerning allegations of child abuse at the heart of Westminster were destroyed in the last few years, according to the report, although not by anyone directly connected to the allegations, it said.

Responding to the report's publication Ms May told MPs: “There might have been a cover-up. I cannot stand here and say the Home Office was not involved in a cover-up in the 1980s and that is why I am determined to get to the truth.”

Peter Wanless, the chief executive of the NSPCC, who led the review, said a sophisticated cover-up was “unlikely” to have taken place. He also said he had not uncovered any attempts by the Home Office to conceal child abuse and that the missing files were last seen “in this century”.

Investigative journalist Don Hale told the BBC that the former Employment Secretary handed him a dossier containing sexual abuse allegations in the 1980s but that his home was later raided by Special Branch, who took the file away. Its whereabouts remain unknown. Ms May confirmed Scotland Yard will investigate Mr Hale’s claim.

Mr Wanless told MPs he had “major concerns” about record keeping by both the police and the Home Office. Speaking to the Home Affairs Select Committee this afternoon about the report’s findings, he said the department’s record keeping was “a mess” and that his report contained “a number of caveats” because information was so difficult to piece together. Mr Whittam told MPs that the pair could not say for certain there had been no cover up but that should not be interpreted to mean there was one.

Mr Wanless said police forces during the period in question only kept paper records on file for up to two years unless a charge was brought. He called it an “imperfect system” pointing out it may take longer to substantiate allegations and that often their significance emerges only when a pattern emerges.

Mr Wanless also said in his report there was no evidence to suggest the Home Office had funded the Paedophile Information Exchange (PIE), the pro-paedophile activist group established in 1974 which lasted 10 years until it was disbanded. Mr Wanless said he had been unable to determine whether or Special Branch funded the group, via the Home Office budget in order to keep track of members. Mr Wanless said that would be “odd but not impossible”.

The investigation endorsed the recommendations from the original civil service report into the missing documents from 2013 about how to deal appropriately with child abuse allegations, which Ms May said the Home Office accepted.

Responding to the Wanless Report, Ms May said she is determined that appalling cases of child abuse should be exposed so the perpetrators face justice. She welcomed the detailed investigation and has written to Mr Wanless to find out whether the security service received any material connected with the missing files was passed to them and if so what action they took.

Rochdale MP Simon Danczuk dismissed the Wanless report as a “whitewash”. He said: “We desperately need to snap out of this overly cautious and defensive approach and see an appetite to confront the cover-ups of the 1980s, not just gloss over the past and hope it all goes away. Theresa May has a once-in-a-generation opportunity to address child abuse failings of the past, but so far all we’ve seen are whitewash reports and hopeless attempts to manage and contain an historic child abuse inquiry.”

Geoffrey Dickens’ son Barry said he was “not surprised” by the findings and questioned whether six weeks was long enough for Mr Wanless to conduct an appropriate investigation.

David Cameron said: “It’s important [the report] says that there wasn’t a cover-up… some of the people who’ve been looking for conspiracy theories will have to look elsewhere.”

Peter Saunders, founder of the National Association for People Abused in Childhood, rejected the Prime Minister’s advice. He said: “Perpetrators are still protected at the highest levels and I think it's disgusting. It goes right to the top. It’s just a sordid issue that everyone has tried to keep under the carpet because it’s too big.”

Mr Wanless’s findings are due to be used by the wider Hillsborough-style inquiry into paedophile activity linked to public bodies and institutions. The Home Office has begun the search for a third chair after Fiona Woolf became the second candidate to step aside from the job. It emerged she lives a few doors away from Lord and Lady Brittan and has dined with them on several occasions.