James Cecil Spencer Ponsford was born on 19th October 1900 at Newlands, near Cape Town, South Africa:

He was the son of Spencer Gooch Ponsford and Lilian Constance Thompson, who had married in 1898 in Amersham, Buckinghamshire. Spencer was a company secretary.
The social standing of the family was such that he was baptised in St George’s Cathedral, Cape Town.

James was the eldest of four children (three younger sisters). When the next child was born in 1906 the family seem to have been back in Amersham. However, in the 1911 Census James was a boarder at The Beacon School, Church Road, Crowborough, Sussex.

Photo posted by Brian Nye, Memories of Crowborough page on Facebook (link)
Between 1911 and 1915 the family moved to Bearsden; the first address I can find for them is North Erskine Park renting a villa called Donbank which is number 15.

James initially attended Glasgow Academy, but soon after he was at Fettes College, Edinburgh, and subsequently went to Glasgow University where he was a well-known athlete – runner, cricketer, and rugby player.
By 1918 when his youngest sister was born, the family was at a villa on Collylin Road, Bearsden, called Craigower, which I believe is now number 3. It was here that Lilian (James’s mother) started Drewsteignton School in 1922. The Ponsfords moved to accommodation purpose-built for the school on Glenburn Road in 1924 (now Upper Glenburn Road). This very successful private school merged with the High School of Glasgow in the 1960s after Lillian’s death.

This is a recent photo of the building the school occupied on Upper Glenburn Road (photo credit: Retties Estate Agency), but it’s also interesting to see a map from a few years after it was built:

I have not found a record of James serving in the First World War although his 18th birthday was less than a month before Armistice Day so he may have been conscripted for a short period of time.
After the war he moved to London to join a petrol company and while there he played rugby for London Scottish.
By 1927 he was stationed at Ipoh in Malay States, presumably still working for the petrol company. He became interested in civil aviation and qualified as a pilot and instructor.

Ipoh is north of Kuala Lumpar
While in Malaya, he married an American, Helen Gatti in 1929. They had at least two children, Anne Lilian (1929), Anthony James Spencer (1934), possibly one other daughter.
At some stage in the late 1930s, the family may have settled in Scotland, in Comrie, Perthshire, while James continued to travel with work. He was home on leave when war was declared and he volunteered for the RAF despite being 40 years of age.
In 1944 he was a Flight Lieutenant with 357 Squadron. They were based at Digri, Bengal (the red circle on the map below), and their purpose was to supply Allied troops operating behind Japanese lines in Myanmar (known to the British as Burma at the time). Flights could involve a 3000-mile round trip and would not have been escorted by fighters.

I imagine James could easily have used his age (now in his mid-40s) to avoid active flying – for example, we know he was President of the Mess Committee (the social secretary). But on 15 March 1944 he was the wireless operator on a long-distance flight made by Hudson III AM949.

The mission was to drop supplies to a Secret Intelligence Service (SIS) team in Kokang, near the border with China. (SIS later became MI6). This paintwork gives an idea of what this type of mission would have involved:

Artwork by Rich Thistle, note the plane depicted is a Liberator which replaced the ageing Hudson
The location was found but it was a night-time drop (at 3am) and “after dropping containers … [the plane] had turned sharply to port to avoid the crest of a 6,000 ft ridge, but it then struck several trees on a lower ridge … The outer part of the starboard wing was ripped off. The nose of the aircraft struck the summit of the ridge and the machine came to rest”.
Only James and one other crew member survived and both were badly injured. The SIS team sent a message about what had happened and the location. A few days later a flight from 357 Squadron dropped a doctor and a sergeant by parachute to help but by this point James had died of his injuries. After a long trek, the other wounded survivor was returned to Allied lines. (For more details of this incredible rescue see link).
James is commemorated on the Singapore Memorial, with 24,000 others with no known grave.

Footnote: Helen’s family
James’s wife, Helen’s family deserve a little more description. Her father was born in London and named Stefano (anglicised to Stephen), youngest son of Angelo Gatti, an entrepreneur: “The Gatti family had built up a large family business in Westminster, including the Adelphi and Vaudeville Theatres, a string of cafe-restaurants and the Charing Cross and Strand Electricity Supply Corporation Ltd, which supplied power to most of the West End of London.” (link) When her grandfather died, the business was run by her uncle John (born Giovanni), who subsequently was knighted and became Chairman of London County Council.
Her father seems to have been travelling in his early 20s because he married Annie Tracey Cornell in Philadelphia in 1901. Helen was born there on 22nd January 1903 (in her father’s army papers her name is spelled Hellen), and they were still there in 1907 when a younger sister, Margaret, was born (possibly February 3rd).
In a letter, her mother Annie says that in 1914 she was living in Brussels, Belgium, and when war broke out she left only shortly ahead of the advancing Germans – it’s not clear if her children were with her.
Helen’s father served in the army in the First World War, then the family lived in Eastbourne before settling in Devon, at Topsham just south of Exeter. Initially they lived at 1 Higher Shapter Street, then at Conifers.
In the 1921 Census Helen and Margaret are together as full-time boarders at the Franciscan Convent School, Silver Street, Taunton.
But the story is not quite over – Annie, Helen’s mother, had been married before to Henry Meiggs Cornell. Henry was the son of a wealthy industrialist and when his father died, Henry inherited £25,000 in 1884 (about £4m today). With his brother he took over running the company and was paid £2,000 a year but in 1889 he was sent on an unlimited holiday because of his behaviour. He came to London and married Mary Rose Brotherton in 1890; she was a servant aged 27 with a daughter born ‘out of wedlock’. They went back to New York where his brother gave him a second chance, employing him for £4,000 per year, but again it did not last and in 1892 he was on his way again.
Mary Rose died in the south of France in January 1895 and it seems Henry had left her, because at about the same time he married Annie Elizabeth Tracy in London. She was American-born (2nd June 1869 in Wrentham, Mass.) but it is not clear how long the marriage lasted because we next find Henry in … the bankruptcy court where it is mentioned he had married twice and had left both women. He had spent the £25,000 and run up debts of nearly £9,000. This was a combination of gambling, playing the stock exchange and ‘fast living’. In 1898 he was on a small subsistence from his mother and 1900 he died in London of syncope (heart disease) aged 35.
Annie returned to the USA where she met and married Stefano, Helen’s father, ten years her junior.
The missing person is Margaret, Helen’s younger sister who vanishes after 1921. She married Donald Percy Stokes in Exeter in 1926.