Every year, in November, “aunt” Charlotte would send me my Christmas present. It was always the same: a thick, leather-bound Smythson diary with gilt-edged paper. She would buy one for each of her six godchildren and, before posting them, made her own entries for events she felt we should know about. She included her birthday on April 1, followed by those of Her Majesty the Queen and the heirs to the throne. She wrote a reminder about the date of the State Opening of Parliament, the Sovereign’s Birthday Parade, the Garter Ceremony, the Cheltenham Festival, the opera season at Glyndebourne and the Isle of Man TT Races (which she went to every year).

On my birthday page in February she would write exhortations concerning good manners, physical fitness and recommended reading matter. When I was 10, she wrote: “Learn to ride and find yourself a decent hunter.” She always slipped a theatre ticket and a fiver into the pocket at the back. These diaries were kept together on their own shelf and she would inspect them whenever she came to visit, expecting to see an entry for every day.

On my 12th birthday she took me to Trooping the Colour, for which she had seats at Horse Guards. I was entranced by the mounted bands and the magnificence of the Life Guards and the Blues and Royals – the regiments that make up the Household Cavalry. It was the start of my fascination with military horses.

In the 1960s, when I lived in Chelsea and thought of myself as a budding boulevardier, I came across the Household Cavalry rehearsing early one day at 5am. The sun was rising and I was strolling home through Hyde Park. It was the 40th anniversary of the Queen’s birth, and the Blues and Royals were already out on Rotten Row. These troopers were in full state kit, tall in their saddles, the chargers kicking up the dust. I could hear the clink of harnesses and the thud of hooves. There were 50 horses, all black, all in perfect harmony. It was a vivid spectacle, with the plumed helmets glinting in the early light.

I remember feeling ashamed that I had spent most of the night drinking in some club and had emerged like a rat into the West End to find myself in the presence of the guardians of the sovereign. They’d already polished their high boots and armour and were out doing their jobs, while I hadn’t even been to bed. I sat on the grass, lit a cigarette and wondered what it must have been like to own a charger or ride in a cavalry charge.

The last serious mounted engagements were in the final days of the first world war, when squadrons from the Blues and Royals were sent into villages in northern France to flush out teams of enemy engineers laying mines. During the 19th century, squadrons of cavalry galloping towards guns protected only by light armour and sabres were a symbol of human and equine courage. It’s almost unimaginable now, but the British employed more than 1m horses in the first world war, and only 65,000 returned home.

Today, the nearest one can get to a cavalry charge is to go hunting with hounds in Ireland. The horses are bred to be bold and fearless and happy to thunder flat out across rough country with no idea of what lies on the other side of hedges and in rivers. The army also prizes these qualities, and still sources many of its horses there, mostly Irish draughts and hunters. They are bought from dealers who specialise in animals with the right colour, conformation and temperament for ceremonial duties. When the time comes for them to retire, the unit’s records bear witness to the multitude of events they have attended.

Horses that have been retired from the military are much in demand, as are those that have left the police force and the turf. Amanda Soden looks after Strobilus, a handsome eight-year-old gelding previously owned by Godolphin (the stable of Dubai ruler Sheikh Mohammed bin Rashid al Maktoum) and trained by Michael Jarvis and Saeed bin Surroor. An injury put an end to his promising career, but only after he had won races in Dubai and Italy and earned, in a few short months, £102,000 on the flat. Strobilus came to Soden through Darley Rehoming, an organisation dedicated to retired racehorses that wanted to ensure he was looked after properly in his later years. Now he lives in rural comfort in Suffolk, where she rides out on him, and Darley comes to check on him from time to time. Personally, I would think carefully before acquiring a high-octane racehorse like Strobilus. These animals are the Ferraris of the equine world, and you need to be certain about what you’re taking on prior to even considering putting your foot in the stirrup.

British police forces employ horses in a variety of roles, and occasionally retired animals will come on the market. Depending on where they are based, tasks might include crowd control at football matches in Strathclyde or formal duties on The Mall, so their training has to be wide ranging. Like cavalry horses, the police’s will be beautifully looked after throughout their lives – although there is no centralised scheme determining where they end up after retirement.

The rarest and most beguiling of all equine acquisitions remains the Household Cavalry charger, and there is now a clear-cut procedure for those who aspire to become owners. Chargers are fundamentally important in state ceremony, and they are strong, impressive, biddable animals that can serve for up to 20 years. Shortly before they retire, they come up for sale.

Lieutenant Colonel Richard Pope is commanding officer of the Defence Animal Centre (DAC) in Melton Mowbray and is in charge of acquiring and training the horses employed by the British army. In 1902, the War Department procured 360 acres of land for the use of military horses and the men and women who look after them. Today, this is the site of the DAC, which trains riding instructors and farriers for the mounted regiments, along with veterinary staff who are attached to them (plus dog handlers and trainers for bodies such as the RAF Police). It is also home to up to 230 dogs and 400 horses. The younger horses marked for a life of ceremonial duty are set to work with older, more experienced chargers. They are trained to deal with the noise and alarms that occur during state events and the crowds who come to watch them.

On average, 18 to 20 horses are retired each year from the Household Cavalry and the King’s Troop Royal Horse Artillery. The first step to acquiring a retired officer’s charger is to put in a written request to the commanding officers of those ceremonial units or the DAC (the sale itself must be authorised by the centre). The DAC, in conjunction with the unit employing a horse that is about to retire, discusses the applicants to identify good matches. As part of the vetting process, they might also talk to applicants to find out how experienced they are, check backgrounds, examine stabling and paddocks, decide whether they are able to handle the responsibility of looking after an army horse, and make sure they know what they’re taking on.

After an application is approved, the prospective owner is invited to one of the ceremonial units to see the horse, because they are prepared for retirement while they’re still working in the regiment. The officers’ and troopers’ mounts, the cavalry blacks, are highly sought after, as are the greys ridden by the trumpeters who would accompany the field commander in battle. The Shires and Clydesdales used as drum horses tend not to be sold after retirement (there are only a few of them, and they aren’t suited to riding). Irish hunters and cavalry mounts are a different matter, however. “They’re solid, reliable, scared of nothing and need minimum maintenance,” says Pope. “These animals are thoroughly trained in ceremonial duties. They are versatile and intelligent and brush up well if you want to show them or use them for dressage or hacking out.”

The buying process can be tense. The DAC may have a dozen or more people interested in a particular horse. Everyone is given full disclosure on the animal, which includes health and training reports from the veterinary and riding staff of the DAC. Then, after the viewing and when all parties are happy, they run sealed bids. Pope is tight lipped about the prices buyers pay, but says sealed bids are the only practical and fair way to make the sales, which are generally held after the ceremonial season ends in late autumn. Those who are unsuccessful the first time and want to try again may stay on the list.

Horses that have injuries or veterinary conditions or are no longer fit to be ridden are retired to charitable organisations such as The Horse Trust at Speen in Princes Risborough. One horse there stands out. Commando was, in his day, the classic officer’s black charger. He was born in Carmarthenshire in 1997 and obviously bred for hunting. Five years later the army bought him for £4,500 on the advice of the DAC, and he joined the Household Cavalry as a “remount” (reserve mount) in the Blues and Royals. In 2003, after the Queen’s Birthday Parade, he fully passed out into the troop. Commando took part in all the ceremonial parades undertaken by the regiment. He was stationed at the Household Cavalry training wing in Windsor, where he was put on “Khaki Ride”, a course that every Household Cavalryman has to complete. “This meant,” according to Pope, “that Commando helped to train and successfully pass out hundreds of new recruits to the Household Cavalry.” The regiment also used him for the “Kit Ride”, which is the last part of mounted dutymen’s training, when they ride in full state kit for the first time. He took part in the Royal Wedding, Gold and Diamond Jubilees, and has been a standard bearer and an officer’s charger. He retired when he started to show signs of arthritis, after 10 years with the Blues and Royals.

According to Pope, “although he tends to be tetchy about horseboxes, Commando has a particularly good stable disposition”. In other words, he is an amiable animal, which is why he was so popular with 1 Troop of the Blues and Royals. He is a very big beast, at 17.3 hands, and has been an asset in the Richmond Cup, where troopers compete to find the smartest man on parade in the regiment. “He brightens up the shabbiest of paddocks,” says Catherine Napper, fundraising manager at The Horse Trust.

As I was leaving Melton Mowbray with my application form and sealed bid offer ready to be filled in, Pope told me that personnel serving in Afghanistan are trained how to use horses as pack animals.

Perhaps there will always be a need for horses in the British army. They’re a national asset, expertly trained and beautifully looked after. And I want one.