Four years ago tomorrow, James Young's life changed for ever in a freak accident when he fell under a train.

As well as sustaining multiple injuries - including collapsed lungs, a fractured skull and face, rib fractures and cracks in his spine - he damaged his left arm while his left leg was severed below the knee at the scene.

James, then 22 and working as a biological scientist, had been about to board a Docklands Light Railway train in East London for a night out with friends.

James Young, 26, from London, became 'part cyborg' in experiment that fitted him with prototype bionic arm

Walking too close to the platform edge as the train pulled in, he had put his hand out to push the button to open the doors. But the momentum of the still moving train caused him to spin and lose his balance.

He fell between two carriages. 'My friends looked round and couldn't see me,' he says, having pieced the incident together from CCTV footage, as he has no memory of it.

'The train stopped and my friends got on it and pulled the alarm. Two men helped them to look for me. The guy who found me, David Kelly, climbed under the train and talked to me to keep me conscious.'

An air ambulance helicopter took him to the Royal London Hospital, where his parents - Philip and Karen, retired City of London Police officers - and sister Elle rushed to be with him.

He was kept in an induced coma for 12 days to protect his brain and stabilise him. At first, surgeons removed dead tissue infected by dirt and oil from the train tracks, but were eventually forced to amputate his left arm.

'Initially, my parents had been told I had broken my leg and arm. They didn't know how bad it was until they saw me,' says James, who needed 12 operations to rebuild his face and body.

Four years ago he fell under a train and suffered injuries including collapsed lungs, a fractured skull and face, rib fractures and cracks in his spine - as well as a damaged left arm and severed left leg

After three and a half months in hospital, he was discharged to go home with a standard issue NHS prosthetic leg and arm, which he describes as 'ugly - peach-coloured and obvious'.

More importantly, the arm had limited capabilities, with a hook instead of a hand.

'And the prostheses are operated by straps and strings, which is uncomfortable to do on a traumatically amputated stump,' he says.

Though the prostheses were better than no left arm and leg at all, such manipulation difficulties just caused him new problems.

To add to his woes, James found it hard to return to full-time work - especially as he had phantom limb pain and had to take heavy-duty painkillers, which left him fatigued.

He was, he says, 'in a dark place'. 'I kept trying to measure myself against a fully-bodied, healthy, able human, which was unreasonable.'

I didn't want to look like The Terminator because my job involves talking to doctors about the drugs they use. I didn't want to look as if I'm going to kill someone

A year ago, however, James's life changed again - this time very much for the better - when he became 'part cyborg' in an extraordinary experiment that fitted him with a prototype bionic arm.

James, a video games fan who uses his good right arm to play, answered an online advertisement from gaming company Konami, which was looking for an amputee interested in road-testing a futuristic prosthetic limb.

It combined ground-breaking robotics, connected to nerves and muscles in the shoulder, with state-of-the-art aesthetics to provide a unique design that reflected the wearer's personality.

Thanks to James's enthusiasm for video games, he fitted the brief.

His bionic arm was fitted at the London studio of prosthetics artist Sophie De Oliveira Barata, creator of the Alternative Limb Project.

Sophie, who has worked on special effects for films, designed James a bespoke metal arm with an attached plastic articulated hand worked by muscles in his shoulders.

The muscle signals are detected by sensors attached to the skin of his shoulders - the sensors are connected to a harness across the top of his body that then operates the arm and hand, all powered by battery.

His bionic arm was fitted at the London studio of prosthetics artist Sophie De Oliveira Barata

Sophie was responsible for the overall look, with another company, Open Bionics, making the robotic hand using a 3D printer. Standard NHS prosthetic arms have a hook or pincer-like gripper.

But James's new hand moves - and feels - more like a real hand and can be cleverly controlled to pick up the tiniest objects, such as a coin, thanks to the 'commands' sent by the shoulder muscles communicating with the sensors.

As James puts it: 'It gives me a hand - and not a device. It's soft, but firm, so it's really nice to shake!'

The cyborg-style arm also features a laser light (for effect rather than any practical use), a torch (to help him find his way around at night), a USB port (in the wrist opening behind the hand) to charge his phone; a watch and even a drone (fitted on a panel on the outside of the shoulder).

It's inspired by a character called Snake, a maimed action man from the game Metal Gear Solid. Clad in sleek silver body armour, the whole effect is like something out of a sci-fi movie.

Getting the look of the arm right was important.

The prosthetic limb combines ground-breaking robotics, connected to nerves and muscles in the shoulder, with state-of-the-art aesthetics to provide a unique design that reflects the wearer's personality

'I didn't want to look like The Terminator because my job involves talking to doctors about the drugs they use. I didn't want to look as if I'm going to kill someone,' says James, whose part-man, part-machine new life with his robotic arm is explored in a new BBC3 documentary, which is available to view online from tomorrow.

At 6ft 5in, James cuts a striking figure with his new arm. Down-to-earth and sunny natured, what really marks him out is his complete lack of self-pity.

'I don't know what to say when people tell me my attitude is good; it's not good, I'm just doing it,' he says.

'If stuff is harder to do, it just means you haven't yet figured out a way to do it.'

The surgeons bore out some bone marrow and slide in a metal rod instead, so your bone cells can start to integrate with it

For all the benefits of the arm, he can't wear it all the time: as well as taking it off to shower or sleep, he has to have a rest from the weight - at 4.7 kg (10lb) with the battery, harness and the layers of heavy gel used to mount the prosthetic arm on the skin of his shoulder stump, it's heavy.

And since it's a prototype, it needs to go in for regular fine-tuning, like a car being serviced.

Designs for fully articulated cyborg legs and feet are even further advanced than hands, because legs are more at risk of being severed in accidents. James is planning the next stage of what could be termed his bionic body-building by getting titanium implants in his left leg and shoulder, which will strengthen both areas.

For remarkable though the hand is, it hasn't yet reached its full potential because of the 'primitive' way the robo-arm is attached to his body.

If that could be upgraded with titanium implants so the arm slots into this directly, he says it could transform his new hand's ability to lift things or wave like a real limb.

Implants will also give him much more strength.

'The surgeons bore out some bone marrow and slide in a metal rod instead, so your bone cells can start to integrate with it.'

The cyborg-style arm also features a laser light (for effect rather than any practical use), a torch (to help him find his way around at night), a USB port to charge his phone; a watch and even a drone

Implants in the leg would help him bear his weight better while using a standard leg prosthesis - at the moment, it hurts too much to wear it for long, so he uses a wheelchair every day. But these titanium implants will be available only to military amputees in the UK, in trials by the manufacturer announced by the MoD for next year. There are no plans yet to extend trials to civilian amputees.

So James has started a fundraising campaign to get the implants, known as direct skeletal fixation or osseo- integration. Longer term, he could raise enough money to get a cyborg leg, too.

Meanwhile, Open Bionics is trying to get the bionic arm medically approved in the hope of persuading the NHS to make it widely available to amputees in the UK.

The argument is that it becomes cost-effective by saving money on physiotherapy and other treatments a patient might need through their lifetime.

The maker had approached me and asked: 'What's the main problem in your life that you can't do?' ... 'Nothing'

Professor Sethu Vijayakumar, director of the Edinburgh Centre of Robotics and Chair of Robotics at Edinburgh University, believes technology has progressed so fast - with its price also coming down because of 3D printing - that robotic limbs could be widely available for just a few thousand pounds within a few years.

As well as helping amputees, robotic devices are being developed to help stroke patients operate paralysed hands again.

A new life is opening up in more ways than one for James, who recently made his speaking debut at a conference bringing science and technology together.

And he recently received a backhanded compliment - being told that he wasn't disabled enough for a disabled version of a new Bear Grylls adventure programme.

'The maker had approached me and asked: "What's the main problem in your life that you can't do?"

'And I said: "Nothing - apart from not being able to run every day round the London Docks to de-stress like I used to."

'So they picked someone else instead,' he grins.