When a young pupil at Gresham’s School approached Logie Bruce-Lockhart and asked him to sign his absence slip, he found the task a little more difficult than he expected. “He refused to sign my sick note until I spelt ‘diarrhoea’ correctly,” he recalled many years later. The boy would grow up to become Sir James Dyson, the inventor of the bagless vacuum cleaner. Just as well he was not one for bearing a grudge. He returned to Gresham’s last year with a cheque for nearly £20 million to endow a new teaching block and research facility at the school.

Dyson had reason to feel indebted to the school and Bruce-Lockhart, its charismatic headmaster. At the age of nine his father, a classics teacher, had died of cancer and his family was unable to continue paying his fees. Bruce-Lockhart pulled strings, came up with a scholarship, and set Dyson on his way.

If Dyson’s inventions displayed his gift for lateral thinking, then perhaps some of that came from Bruce-Lockhart, who was not a man for committees or minute-taking, nor greatly concerned about length of hair or width of trousers. He was headmaster of Gresham’s, in Norfolk, from 1955 to 1982, the longest-serving in the school’s 450-plus history, during which he oversaw its transformation into a coeducational establishment.

Logie Bruce-Lockhart was born in Warwickshire in 1921, the youngest of four sons of JH (Rufus) Bruce-Lockhart, a teacher, and Mona. Rufus was a housemaster at Rugby when Logie was born. The family moved to Edinburgh when he became headmaster of Cargilfield, and then to Cumbria when he took the same position at Sedbergh. It was at Sedbergh that Logie’s sporting talents emerged. He broke the school record for discus and shot and became head of school.

After the outbreak of war, he began studying languages at St John’s College, Cambridge, before being commissioned into the 9th Sherwood Foresters, an armoured car regiment. When that was disbanded he joined the 2nd Household Cavalry, the reconnaissance unit for the Guards Armoured Division. He took part in the northwest European campaign as a troop commander, where his skills in French and German proved useful.

He was one of the first of the Allied forces to arrive at Belsen concentration camp after its liberation but found many of the inmates “looking like ghosts from Hell, not yet fit for freedom”. Bruce-Lockhart oversaw a refugee camp for 5,000 displaced people, mostly Poles, before returning to Cambridge to resume his studies.

Boarding a crowded train in March 1944, he had struggled to find a seat but eventually settled down in a first-class carriage opposite “an extraordinarily pretty girl in a smart civvy suit”. Her name was Jo Agnew and they bonded over a shared love of Rupert Brooke, whose poetry he was reading on the journey. They were married for 64 years until her death in 2009. He is survived by four of their five children: Jennifer, Rhuraidh, a property developer, Fiona, a retired English teacher, and Duncan, who worked in the City. Kirsty died aged seven when she was run over by a car, an event that affected Bruce-Lockhart deeply.

Returning to Cambridge after the war, he gained honours in French and German, won the Wright prize for languages and was awarded Blues for rugby and squash. On graduation he joined Tonbridge School to teach modern languages and played rugby for London Scottish, eventually captaining the Richmond-based side.

A fly half, renowned for his speed off the mark and a devastating sidestep, Bruce-Lockhart was widely viewed as one of the most skilful players in English rugby. The first of his five caps for Scotland was in the Calcutta Cup win against England at Murrayfield in 1948, but he had to wait two years for his second, against France in 1950. He played once more that year, against Wales, but had to wait another three years before being recalled to face Ireland and England in 1953.

Bruce-Lockhart was just 33 when he assumed the headship at Gresham’s. While his style was enlightened and he was no stern disciplinarian, he had little time for fashionable left-wing educational theories. His school speeches were renowned for being funny and down to earth.

Bruce-Lockhart published books on fishing, birdwatching, poetry and conservation. He was a talented musician with a particular love of Schubert. For a year before his death he held the distinction of being Scotland’s oldest surviving international rugby player.