Police and Suffolk county council have said they no long have files on a joint investigation into allegations of child abuse at a boarding school for troubled boys.

Alexander Hanff, a former pupil of Kesgrave Hall near Ipswich who has alleged he was sexually assaulted by staff at the school, said he was "deeply disappointed" that records of the 1992 investigation appear to have been destroyed. Hanff is one of 10 ex-pupils who told the Guardian they were victims or witnesses of a range of abuse at the school between 1980 and 1993.

At least 30 pupils were interviewed by police in 1992 as part of the Kesgrave Hall investigation. Four members of staff were suspended and received psychiatric help before being reinstated. The school was closed down in 1993, a year after the police inquiry, and no members of staff were prosecuted.

Suffolk police have been urged by Daniel Poulter, the Tory MP for Central Suffolk and North Ipswich, to reopen the investigation after he said he was "extremely concerned" about the abuse claims.

A spokesman for Suffolk police said on Thursday he could not say whether the investigation would be reopened. The force said in a statement: "Suffolk Constabulary no longer holds the files in relation to crimes occurring of this nature at Kesgrave Hall School due to the age of the offence and that review, retention and disposal guidelines at the time scheduled for its disposal."

The Guardian has been told that Vivian Davies, a former director of the private company that ran the school, destroyed the vast majority of records relating to Kesgrave Hall when he moved house before his death.

Hanff, who wrote in the Guardian about abuse at the school, said: "I think police files in cases like this should have been retained and archived appropriately, same for social services and the CPS, specifically because of situations just like this. I am deeply disappointed that the police claim the files have been destroyed, the CPS claims to have never have been sent the case papers.

"Furthermore, the authorities should have advised us of our rights to file insurance claims at the time and should have followed up the investigation with social care, such as counselling or where required more comprehensive psychiatric care. Perhaps then I wouldn't have spent the last 27 years with a chronic sleep disorder and night terrors."

A spokeswoman for Suffolk county council said: "All Freedom of Information requests follow a well defined process and are dealt with in the same way. The county council received and responded to an initial request and subsequently conducted an internal review on behalf of the requester. On both occasions no information was found."