Lord Gardiner was appointed a Companion of Honour in the 1975 New Year's Honours. In June 1981 Gardiner survived a failed assassination attempt when a bomb containing 3 pounds of explosive was attached to his car by the IRA during a visit to Belfast. The device was later found near the junction of University Road and Elmwood Avenue, Belfast, and defused by the British Army. The IRA released a statement saying: "We meant to kill Gardiner, the political architect of the criminalization policy and the H-blocks. The device fell off the car and failed to explode." He was Chancellor of the Open University from 1973 to 1978. In 1925 he married Lesly Trounson (died 1966). They had one daughter. In 1970, Gardiner married Muriel Box, writer, producer and director who had won an Academy Award for Best Original Screenplay for "The Seventh Veil". She published his biography in 1983. He died in Hendon, London on 7 January 1990, aged 89. Gardiner's archives are held by two institutions, the Churchill Archive Centre in Cambridge and the British Library. The latter collection chiefly concerns the abolition of capital punishment in great Britain.