[2] Gilliat's childhood was divided between The Cedars in Chorleywood and Frogmore Hall, Hertfordshire, before moving to the Manor House in Welwyn.
[2] Gilliat served with the Rifle Corps in Northern Ireland and Palestine prior to the outbreak of World War II, and was captured during the Battle of Dunkirk as part of the British Expeditionary Force.
[3] Gilliat was appointed a Commander of the Royal Victorian Order in 1954 after his assistance during the Australian visit of Queen Elizabeth II and Prince Philip, Duke of Edinburgh during February 1954.
Queen Elizabeth had been widowed for only three years when Gilliat entered her service at her London residence of Clarence House, his obituary in The Independent credited him with helping her carve out a new role for herself and described his attitude: Like her, he took a genuine interest in the lives and doings of all with whom he came into contact and made them feel that they were important to him.
He had been reluctant to leave her service, having worked for her for several months after his diagnosis of cancer despite his ailing health,[7] and he remained in his post until three days before his death.
[7] The portrait painter Andrew Festing likened Gilliat and the Queen Mother's relationship to that of brother and sister, saying that the pair bickered good naturedly.
[9] Gilliat appointed a Deputy Lieutenant of his native county of Hertfordshire in 1971, and made an honorary Bencher of the Middle Temple in 1977.