At different times in a varied and what he regarded as an often amusing life, Robbie Leith-MacGregor wore the uniform of all three Services. He had hoped to follow his stepfather into the Royal Navy but, while at Pangbourne, it was decided he was unlikely to reach the standard in mathematics, so he went to Sandhurst instead. He won his DFC with the Royal Air Force and his Military Cross with the Army in separate wars.

Commissioned in 1938 into the Royal Northumberland Fusiliers — the “Fifth Fusiliers” as they were known from their number in the Infantry of the Line — he accompanied the 2nd Battalion to France with the British Expeditionary Force just after the outbreak of war. He missed the debacle of Dunkirk because he was seconded to the RAF for pilot training in April 1940.

It was intended that after qualification as a pilot he would be engaged on Army co-operation work. Having gained his wings, he seized the opportunity to join a squadron flying Lysanders in support of the Eighth Army in the Western Desert. Subsequently, he transferred to No 208 Squadron flying Hurricane and Tomahawk fighters and it was with this squadron that he won his DFC in June 1942.

While on reconnaissance patrol in the area of Bir Hacheim, after the Eighth Army’s abandonment of the Gazala Line, he was “jumped” by four Messerschmitt 109 fighters, which attacked him in turn. Displaying airmanship which he afterwards protested he had no idea he possessed, he countered each attack and shot down one of the Messerschmitts. The remaining three pursued him towards El Adem, where his aircraft crashed in flames. Climbing out unhurt, he was amazed to find himself in the forward positions manned by soldiers of his own regiment.

He was less fortunate in a later engagement and shot down over El Alamein before the decisive Eighth Army advance, taken prisoner and held, first in Italy and then Germany, until the end of the war. His secondment to the RAF completed, he rejoined the 2nd Battalion of his regiment in Greece in December 1946.

In 1950 he accompanied the 1st Battalion to Korea, where they joined 29th Independent Infantry Brigade Group under the command of the US Eighth Army opposing the North Korean invasion. Leith-MacGregor was in command of Y Company. (As a former medium machinegun regiment, the Fifth Fusiliers titled their companies W, X, Y and Z to distinguish them from the companies of infantry battalions to whom they gave supporting fire.)

Until very shortly before new year 1951 the line of the Imjin river was being firmly held by one US and two South Korean divisions in anticipation of a big Chinese attack. This began at 21.30 on New Year’s Eve and, some ground having been lost in one of the South Korean divisional areas, 29 Brigade was ordered to mount a counter-attack. When it was discovered that the enemy penetration was deeper than at first thought, the brigade was switched to a defensive blocking position. Leith-MacGregor’s Y Company was made responsible for the key feature on the left of the battalion sector — Hill 280, which rose about 600ft above the road along its western side.

At 17.15 on January 3 the Chinese attacked the centre of the Fifth Fusiliers’ position. The deserted village immediately in front was overrun, and a number of snipers penetrated between the forward company positions and on to the rearward slopes of Hill 280. From there they were able to keep up a harassing fire on to the rear of the centre company and, having been joined by two machineguns during the night, to dominate a key track junction on the battalion’s lateral communications.

The assault on Y Company’s position began at first light and continued during the whole of that day. But Y Company had been well trained by Leith-MacGregor and everyone had complete confidence in his judgment. Throughout the action all attempts to dislodge him were frustrated owing to the skill with which he had sited his company and the determination with which he inspired his men to hold it. Confidence in him was shared by the Fifth Fusiliers’ commanding officer, who was convinced that Hill 280 would not fall so long as men of Y Company were left to defend it. When the order for the battalion to withdraw was finally given, Leith-MacGregor brought out his company without the loss of a single man. He was awarded the Military Cross.

Robert Leith-MacGregor was the only son of Frametta Burle, whose second husband, a rear-admiral, had encouraged him to try for the Royal Navy. After his service in Korea he was second-in-command of 3rd Battalion Royal Nigerian Regiment and commanded 1st Battalion the Fifth Fusiliers in Hong Kong and Germany 1960-63. As the nearest he had come to the Staff College was, in his words, when co-opted to keep goal for the Camberley hockey team while at Sandhurst, he decided that his military future would be limited after commanding his regiment, so he left the Army.

He was a representative for Guinness in London for some years and later marketing and sales director for Rank Hotels and the Park Lane Hotel.

He was married to Pamela, the daughter of Sir Nutcombe Hume, in 1945. She predeceased him and he is survived by one daughter.

Lieutenant-Colonel Robert Leith-MacGregor, MC, DFC, was born on August 23, 1917. He died on November 14, 2008, aged 91