Appointed as Her Majesty's Chief Inspector of Prisons by Douglas Hurd, Tumim soon made a reputation as a critic of the existing system. He campaigned successfully for an end to slopping out, and was also critical of the "enforced idleness" of prisoners, and poor mental health care. He served under successive Conservative Home Secretaries (not all of them sympathetic to his views), until Michael Howard declined to renew his contract in 1995, and David Ramsbotham was appointed. He was knighted soon afterwards, served on many charitable trusts, and continued to inspect prisons overseas. He was the founding President of UNLOCK, The National Association of Ex-Offenders. Between 1996 and 1998 he was principal of St Edmund Hall, leaving amidst some controversy (he was popular with students, less so with academic colleagues). He was High Steward for Wallingford from 1995 to 2001. Tumim was named "Oldie of the Year" in 1994 by The Oldie magazine.
Tumim was on the committee and a buyer for the Contemporary Art Society. Between 1990 and 2003 he was President of the Royal Literary Fund.
| Her Majesty's Chief Inspector of Prisons