MY great uncle's letters from the Front are written in looping handwriting on yellowing blue-lined foolscap.

I am looking at them now: a sepia bundle about a centimetre thick on my bright white Ikea desk. They look and feel antique - some of the sheets are like sheer fabric from having been read countless times - but as I sit alone in my office turning over the pages, reading about my uncle's delight at the fruitcake he has received from home, sharing his pleasure in new friendships and sensing his restrained fear, the years melt away and Stuart Chadwick becomes so real I feel I could turn around and he would be standing in the doorway.

My grandmother's eldest brother was 19 in summer 1916 when he was sent to France. He was the first of five siblings and, by all accounts, the shining hope of the family. The Chadwicks lived in the mill town of Bradford, West Yorkshire. After signing up, Stuart went to training camp in Staffordshire with a group of lads from Bradford and they stayed together like an unofficial pals' brigade when they were sent "Somewhere in France", as Stuart always headed his letters after June 1916.

The young man who emerges from the pages is gentle, plain-spoken, not at all worldly like modern teenagers but highly conscious of his position in the family and making an effort always to reassure, even when writing from dim dug-outs. In spring 1916, when he is still in England, the letters convey his high spirits - hoping to be accepted on to a course to be a rifle shooting instructor and quipping that the corporal says they'll be shot at dawn if they're caught sweating while digging trenches - but this noticeably falls away after his arrival in France.

There have long been unanswered questions about Stuart. Researching his story has allowed me to fill in some of the gaps and, above all, to better understand how the events of that year affected our family.

Stuart was born on December 5, 1896. His father, my great grandfather Walter, made a modest living from a printing press, which my great grandmother, Rebecca (after whom I am named), supplemented by running a small greengrocer's out of her front room. After Stuart, they had four more children: Emily, George, Jessie (my grannie) and John.

In January 1911, aged 14, Stuart became an office boy for the Bradford Hospital Fund Executive Committee, working five-and-a-half days a week for five shillings (25p). A committed Christian, he met a girl, Ruby, through church; he was courting her when he signed up.

According to his 1915 appointments diary, he was 5ft 6in tall and weighed just under seven stone. Today, he would be described as seriously underweight, but at the time, northern recruits were often said to be undersized. Stuart was in an office job, but he and his family were not well off. The chimneys of the mills, where his brother worked, belched out smoke which everyone inhaled.

So when we look at his picture in soldier's garb, the thick woollen fabric rather swamps him and underneath the peaked cap is a painfully young face, a lad looking ill at ease in a man's uniform. Hard to believe that this mere boy, early in the war, had been handed a white feather; he had promised his mother he would not sign up until he was 18.

He arrives in Brocton Camp, Staffordshire, in early April 1916, sounding upbeat. His letters are full of contemporary teenage slang: "I am in the pink"; "the contents of the parcel were A1"; and - describing the treat of having tinned sausages for tea one night - "we were doing it large".

His family is in near constant contact with letters and parcels. Currant cakes, chocolate biscuits, toffees, buns, new pencils, pens and pads, the occasional pair of socks, hankies or puttees; even, at one stage, a fresh cucumber, sent all the way to France at the height of summer: tokens of affection arrive in a steady stream.

His constant preoccupation is food: having eggs, bread and butter for supper is "champion" and he is thrilled with sardines and beans for tea. He describes various duties, such as steaming blankets clean and learning to shoot. Cheerfully thinking ahead, he writes: "I will be able to do nearly anything when I finish in the Army. If I can't get a job at anything else, I can get a Navvies job, I can use a pick + shovel alright now." The Western Front must at this point seem very far away.

Has he heard rumours of an imminent big push in France? We can't know, but on June 23, he is sent to Clipstone barracks in Nottinghamshire and assigned to the Duke of Wellington's regiment. He and his friends are issued with new equipment, amid rumours they will soon be shipped out. He writes: "I hope you will not worry about me, as I will write regularly and I have a good lad for a pal, so I will be alright."

The next letter comes from France. It is much less chatty, just passing on address details of his camp at Le Havre. Then, on July 13, he explains that he has been transferred to a new regiment, the King's Own Yorkshire Light Infantry (KOYLI), 10th battalion.

The reason for this is all too clear from the dates. The first day of the Battle of the Somme, July 1, was famously bloody and the KOYLIs were in the thick of it. The 10th Battalion was formed to make up for other KOYLI battalions' heavy losses, though if Stuart knows this, he does not say so.

On July 27, Stuart writes in what sounds like a concerted effort to reassure his parents. "I am pleased to say I have had the best of luck out here," he says, adding that he is now in the Lewis (machine) gun section with three pals and has "nothing to grumble about". A few days later, on August 2, he asks for a French dictionary, since "it is awkward when ...you can't speak to them properly".

Then come two letters that for the first time hint at his fears. "I will not be sorry when the war is over," he writes to Emily, on August 7; and to his parents: "So Cyril [his friend] is finding it heavy, is he, well he wants to stick it, as ... he is in England, and that is a lot to say. I have had it pretty rough at times, but at the present time I am going on alright."

Four days later, he writes to his parents: "We have just come out of the Trenches for a rest, I have gone through it alright. I hope that I may have the luck I have had in the past, then it will be alright."

In late August, the 10th KOYLIs start getting roast dinners instead of stew, though if Stuart sees any portents in these improved rations, he does not express them. On September 7, he thanks his parents for a new handkerchief, and on September 14, writes: "I may not be able to write as regular during the next few weeks, but I will not lose any opportunity to write you, even if it is just a Field Card."

Sounding more cheerful and like his old self, he includes lots of thank-yous to relatives and friends for gifts received, and even teases Emily, a secretary, over an increase in her workload: "I hope Emily will get over the extra work she has to do. As you used to say to me, she must have extra pen nibs to wipe. Well, I had better shut up or she will be telling me off when she writes again. I think that is all I have to say at present, hoping you are all in the best of health, as it leaves me at present. Again thanking you for the parcel."

About a week later, the family receive a Field Card, a postcard with multiple choice options - Stuart has left open "I am quite well".

And that was the last his family ever heard from him.

For a fortnight, the Chadwicks heard nothing, and then a letter arrived. It was from Len Dobson, Stuart's great friend from the gun section, dated September 29. It says: "It is with deep regret that I have to write this letter to you, to inform you that your son Stuart was reported missing after being in action." Len speculates that he may have been taken to hospital.

Two days later, on October 1, Len Dobson writes again: "Just a line or two to say that the parcel addressed to Stuart arrived here on the 30th and as we arranged before going into action to share all parcels out if anything happened, we shared it between his pals."

What must the effect of these letters have been on Rebecca, Walter, Emily, George, Jessie and John? We can only guess. Uncertainty and cruel hope, combined with the darkest fears, must have plagued them. And then comes another letter from Len, dated Sunday, October 29: the letter they must have dreaded.

It says: "I am sorry to say that nothing else has been heard of Stuart and I am afraid that he will now be in his eternal home. Please excuse this letter as my heart is full of sympathy for you all as I know what it must mean to you. As you know I cannot tell you much of what takes place here. I was at the side of Stuart when the order came down the trench to go over the top and attack. It will seem strange to you but when we go over we cannot see anyone but those near to us. Somehow Stuart and I got separated and afterwards when the roll was called he was not there to answer. We made inquiries but no-one seems to know what had become of him and as there was very heavy shell fire at the time, I am afraid he must have been hit by one and probably buried."

Months pass. Autumn turns to winter, Christmas comes and goes, and then in March 1917, almost exactly six months after Stuart's disappearance, Rebecca Chadwick receives a letter from a GG Buckley (Mrs) of the British Red Cross Enquiry Department for Wounded and Missing. It is written in obvious haste, almost scribbled, reflecting, no doubt, the huge number of such letters Mrs Buckley had to write. She says: "Dear Madam, In reply to your letter I fear it would be quite useless for us to give an opinion as to your son's fate after he fell - without knowing more of the circumstances of the fighting. If he WAS buried by the Germans, his name ought in course of time to reach us on one of the "Lists of the Dead" which they send in. I fear he can hardly be alive as a Prisoner, in any state whatever, as if he were unable to write he would still have been reported on a Prisoners List. We are continuing our inquiries but with little hope."

This, to me, is the most heartrending letter of all, because it shows the family still held out the desperate hope that Stuart was a prisoner of war. There had to be a chance - surely?

They do not give up. Rebecca writes again a month later and receives another, even more hasty missive from Mrs Buckley, this time scrawled on a postcard, saying merely that they were "continuing enquiries ... for your son". I know from my mother that a distraught Walter (Stuart's father) went to London in person seeking information.

Did they ever find out the full details? I don't know, but we can now fill in some of the gaps. Stuart never was a prisoner of war and his body was never found. Though his service record was among those of many that were destroyed during the Blitz, the Record Office, which issued him posthumously with the British War and Victory medals, states his date of death as September 25, 1916. It was the first day of the major Battle of Morval offensive. Doncaster Museum, home of the KOYLI archive, holds the regimental war diary and for that day, it says just this: "Battalion attacked trenches east of Gueudecourt under heavy enemy machine and artillery fire, wire was still very strong and Battalion was held up. Casualties: officers, Killed, 7; Wounded, 7. Other ranks, K.43. W.149. M.97."

M.97 - those three digits encapsulate Stuart's fate: along with 96 others, he simply went missing. The KOYLI's curatorial adviser, Stephen Tagg, believes he could have been killed outright by a shell, as his friend Len Dobson, perhaps kindly, suggested; equally, the war diary suggests that attempts to break through the enemy barbed wire failed and the Germans were mowing down British soldiers with machine guns. He may have been shot outright, or, God forbid, left injured and dying in a shell hole.

Stuart's death marked a turning point for the Chadwicks. Lives were jolted and set on different paths because of it. Rebecca Chadwick became depressed and by 1922 had become very ill indeed. Such was the stigma associated with mental hospitals, that her family sent her to stay with her cousin in Darlington instead. When she returned after six months, in December 1922, her depression had abated, but within a fortnight, she died of flu, aged 53. Walter died six months later, aged 52, from hydro encephalitis.

Emily too had a nervous breakdown, in around 1919, aged 20. She recovered, but her depression returned with a vengeance on retirement and she died in 1959 in a mental hospital. The sudden loss of her elder brother, mother and father seems very likely to have contributed to her poor mental health.

Stuart's girl Ruby never married. My mother remembers meeting her more than 25 years later, a slight woman who was always referred to even then as "Stuart's girlfriend".

As for my grandmother, she was remarkably resilient. The loss of her brother and parents by the time she was 19 was not the end of her early traumas. She lost her fiance to tuberculosis in the 1920s. But then she married my grandfather (a widower), became stepmother to his son, and went on to have two daughters. She lived a long and happy life, mostly. She was widowed in 1971, and my mother's younger sister Cathy died suddenly 11 years later. Following Cathy's death, my devastated grannie said that she seemed to lose everyone she loved the most. Yet she always kept going. She was an optimist, fiercely bright and independent, and focused on the here and now.

But she never forgot her beloved brother Stuart. Because of that, neither has the rest of the family. A few years ago, my husband and I visited the Thiepval Memorial to the Missing of the Somme, built to commemorate the 72,195 British and South African soldiers whose remains were never recovered. It sits on a gentle rise in farmland, but its brutal angles and imposing proportions evoke the industrial warfare that once devastated the surrounding landscape. The day we saw it, sunshine set the limestone facing alight, though Stuart's name was in shadow. Like thousands of people over the last 80 years, I stood on the podium and looked out at the fields, wondering where our family's loved one might now lie.