A study suggests that one in six veterans who left the British military after serving in a combat role in Iraq or Afghanistan would probably qualify for a diagnosis of post-traumatic stress disorder (PTSD). In some, the symptoms only appear years later.

On Remembrance Day in 2015, Phillip Riding, had been out of the military for one month. He went to the Cenotaph as a civilian, with his medals from Afghanistan pinned to a white shirt, and sang God Save the Queen with the crowd.

In the silence afterwards, a bugle sounded The Last Post. And in that moment, suddenly the memories of Afghanistan came flooding back.

"Something inside had snapped. I couldn't breathe, I was panicking standing there in the ceremony with tears rolling down my face," Riding says. "That sound of the bugle reminded me of the moment it was announced every time a comrade was lost."

Friends, killed or injured, flashed in front of his eyes: Bing from artillery, Tres shot in the ankle, Rocco, Plant, Coops, LJ shot in the shoulder, Jordan….

For five years he had been suppressing these thoughts.

"I thought I was fine but all of a sudden I wasn't any more. That door I kept shut, opened completely. This is how PTSD is, it's something that creeps up on you. It just totally destroyed me."

Riding joined the Army in August 2007 at the age of 16, partly to get out of his home town, Barrow-in-Furness, in Cumbria. He'd faced homophobic bullying at school and thought a "macho" role in the infantry would help mask the fact that he was gay.

"I was living with these guys seven days a week, and I started copying how straight men moved. My body language was super-exaggerated to be manly because I was trying to fit to this image of who I wanted to be in my head."

He would plaster his bedside with soft porn. "Bikini models were for sure not what I wanted to see first thing in the morning but there we are."

He even put a pretend girlfriend in his will before leaving for his tour of Afghanistan.

In 2010 the British military had the task of curbing opium production in Helmand Province. It was a dangerous job in territory largely controlled by the Taliban.

"Once you've been shot at it never leaves your brain. The bullet that comes near you sounds like a crack of a whip. There were countless operations where I was in a near-death situation, almost blown up in armoured vehicles by improvised devices or ducking shells from our Apache [helicopter]."

Riding wasn't hurt himself, but many were.

"There was a task to go out and do some metal-detecting. We played a game of rock paper scissors to decide who should go on patrol and who should stay behind. I won the game. He went out and was shot in the ankle."

One of his roles in Afghanistan was to drive lorries. Once he went on rest and recreation, and the driver who took his place rolled over an IED and ended up having his back reconstructed.

He was lucky, but being lucky made him feel guilty. "Shouldn't it have been me? Shouldn't I have gone on patrol?" he asks.

Coming close to death made Riding think hard about his life, and he decided to come out and live authentically as a gay man. "It was like being born again," he says. "This time I was being who I wanted to be - myself."

Initially his family didn't take the news well. Around Christmas 2011, when Same-Sex Marriage Bill was passing through Parliament, Riding's younger brother asked if he would get married. His grandmother then said she wouldn't attend the wedding if so, and his mother followed suit. "There was an argument, and I wish that I had handled it better," he says. He left home on Boxing Day.

Coming out to people in the army didn't go well either. Some former friends got up and left when he sat down next to them at dinner. Things only improved after he launched a complaint. Now he decorated his bedside exuberantly with rainbow flags and male pin-ups.

He also found solace in London's LGBT community, travelling up there at the weekends. The gay nightclub scene in Soho was so different from army life, it was a form of escape.

"It was blessing to talk to people who didn't know anything about the military or what it was like in Afghanistan.

"My friends were incredulous, teasing me: 'Seven months in Afghanistan? Just you and all those soldiers, and nothing happened? Yeah right!'"

Being in the army isn't like it's depicted in the movies. "Not everyone is really handsome, dashing. You're enjoying not thinking about romance. From the moment you wake up, you're working and your mind is on the job."

But the high-octane pace of clubbing also seemed to serve one of his needs after the tour in Afghanistan.

"When you have adrenaline pumped into you every single day for seven months, when you come home that's missing. Time moves slow. People moved slowly. It was so quiet. I needed to be in the clubs to fill that gap.

"Being in a nightclub, it's just so loud, the bass in the floor. There is so much energy everywhere - it's sensory overload."

Riding had his driving licence revoked after being caught speeding twice in two years after he returned from Helmand. "Once I was going 85 mph on a 60 mph dual carriageway with music at full blast. Risky stuff like that because it was an adrenaline rush."

He thinks that the excitement of coming out probably helped to mask his PTSD after Afghanistan. "I didn't think I had an issue. I was dealing with accepting my sexuality and meeting all these new people. For the first time in my life, there were people who I fancied who actually fancied me back!"

When it came to renew his contract with the army in October 2015, he decided against it and took up a job as an events manager for a nightclub. He would go into Soho in the day, arrange the events and be ready to work late into the night, while socialising with friends.

But he found himself asking this question: "I've come out, but why am I still hitting the bottle? Why am I still not wanting to go to sleep?"

And a month later, on Remembrance Day, he received an answer.

Riding likens the feeling of suppressing his PTSD to trying to hold down an inflatable ball in water. "It's different for everybody, but this is what it's like for me. I kept trying to hold down all the things I saw and you can only hold it down for so long. The more you hold it down, the stronger the ball shoots back up, more powerful than before. And that's what happened with me."

He started having nightmares about his time on tour and working all night seemed to help him cope.

"I would have flashbacks. I did what I could to avoid closing my eyes in case I started to see Afghanistan," he says. "I wanted to physically exhaust myself, so that when I eventually got home in the early hours, I could just collapse in bed and I wouldn't dream."

The Last Post had been the first sound to trigger Riding's PTSD, but other everyday sounds now had the same effect - a motorcycle abruptly appearing from nowhere or someone yelling in the street.

What does PTSD feel like?
Flashbacks & nightmares: These can be so realistic that it feels as though you are living through the traumatic experience again and again - ordinary sounds, sights and smells can trigger flashbacks

Avoidance & numbing: You distract yourself by keeping your mind busy with an activity or working very hard, while avoiding places and people that remind you of the trauma - and you may try to become emotionally numb, feeling nothing at all

Being hypervigilant: You stay alert all the time, as though you are looking out for danger - anxiety makes it hard to sleep, and others may notice that you are irritable and cannot relax

There was a trigger in the club as well.

"At midnight they have this balloon drop, balloons fall from the ceiling and they bounce on the crowd. The sound it makes is just like gunfire happening over my head."

The first time he experienced it he was frozen on the spot. "It shocked me that even though my brain was telling me I am literally just seeing balloons fall down, I couldn't move because I was panicking."

It got to the point that Riding would leave quickly when the balloon drop was about to happen and his friends noticed. "No-one understood why, because I didn't tell anyone. They just thought I was weirdo, that 'Phil doesn't like balloons.'"

He felt that working in the club brought some order to his life. "I was in the military for years, having that authority, I got used to it. In a way, being that person that people look to in the nightclub for direction is similar."

But the sense of the club as a safe space was shattered on 12 June 2016, when a gunman opened fire at a gay nightclub - Pulse, in Orlando, Florida - killing 49 people and injuring 53 before being shot dead by police. At the time, it was the deadliest massacre in modern American history.

Riding had actually been to Pulse in 2011. "I know the venue and I knew some of the people who were there that night. I think about them pinned down in the bathroom... and having to witness their friends and family being shot and killed," he says.

"It was horrifying, warfare coming into the community I know and love. Before I felt that I could keep the worlds apart but now they are crashing into each other. The idea that a terrorist attack could happen here too."

It wouldn't be the first time, Riding says, mentioning the 1999 nail-bomb attack carried out by a neo-Nazi at the Admiral Duncan, one of Soho's oldest gay pubs.

He started to be troubled by intrusive thoughts, imagining bad things happening to his family and friends. In Afghanistan he had been bothered by the thought that if he had acted differently, a comrade might not have got hurt. Now this kind of thinking became obsessive and infiltrated his daily life.

When meeting a friend for coffee in Soho, he would imagine a bomb exploding in the gay bar next door and his friend dying in front of him. "The questions cross my mind, 'What if they were just late by 10 minutes? What if I had just gone shopping, and they wouldn't have had to come meet me?'

"It never ends. This guilt is unbearable. Not just the guilt of what has happened but even hypothetical situations. So what can I do?"

It took years for Riding to be formally diagnosed with PTSD and start receiving therapy.

For a long time he tried to avoid seeking help, mistakenly believing that a diagnosis of PTSD on his medical record would harm his prospects when applying for jobs. Other soldiers were under the same illusion, he says.

"It's one of those urban legends. We simply didn't talk about mental health to each other so I didn't know. I wish I had known sooner."

Nowadays he makes a conscious effort to rethink the noises that trigger his PTSD. At 27, he's made a conscious effort to associate the national anthem with good times. "It always has me in tears," he says. "I want to think instead about all the good times with all the brave lads."

He says that his sleeping is better now and that he's in control of his PTSD - not the other way round. Trying to bury it, he says, was the wrong idea.

"So if my PTSD is that inflatable ball - it's like it's been deflated. It'll still be here but I'm holding it down for now."