‘Knife to skin.” I’d never heard the expression before. Nor had I heard the crack of a fibula bone being cut in two. But we all hear it. Knife to skin. Bone-cutter to bone. And now a new sound: the urgent buzzing of a power saw.

Mr David Lewis – a consultant vascular surgeon who worked in Christchurch, New Zealand, until the 2011 earthquake obliterated his home – moves the saw closer to the newly formed opening in Kay Watkins’ solitary leg. He positions it just below the knee.

It resembles a regular handheld power drill – bar a rectangular steel blade, serrated at the end, in lieu of the drill-bit. In a matter of seconds, it cuts straight through the other, bigger bone in Watkins’ leg – the tibia. More cutting and cauterising follows. The leg is severed. “Thank you,” Lewis says quietly to his team.

Watkins lies motionless, her face and torso hidden under a light blue surgical drape. She is shrouded, save for a tuft of her hair at the top, beneath the gaze of an anaesthetist.

Her disembodied leg, with its partly blackened, ulcerated foot, is wrapped in a dull-green sterile bag, tied at the top and presented to the theatre nurse. He reaches across and drops it into the “limb bin” of Cardiff’s operating theatre 15, then continues bagging up swabs that are thick and heavy with blood. The bin bears the instruction: “Destroy by incineration”.

Between 2021 and 2022, diabetes was linked to more than 650 amputations in Wales (in England, the number of amputations is more than 9,000). This is Watkins’ second. As the number of patients with diabetes continues to soar, so do the myriad demands on health services. “It is a major public health crisis,” says the charity Diabetes UK, “and it’s worsening at breathtaking speed.”

I met Watkins two days earlier. The 56-year-old, from Blaenavon in south Wales, was on the vascular unit of Cardiff’s vast, sprawling 1960s-built University Hospital of Wales.

During my visit, the unit had 38 patients, with 15 more waiting to be admitted. Astonishingly, nearly half of them had diabetes – a condition characterised by high blood sugar levels when the body can’t produce any or enough insulin, or the insulin doesn’t work properly. Watkins has had type 1 diabetes since childhood. Nearly all the other patients have type 2, which is often preventable and commonly associated with obesity, low physical activity and old age.

“All the arteries are furred up inside,” Watkins tells me, propped up in her hospital bed, glancing towards her outstretched leg. “There’s no circulation to my toes to give them oxygen. It needs to come off – like my other leg.”

The sole of her now redundant foot is rough, red and scabrous. Two of her toes are black; tissue appears to be missing, sacrificed to gangrene. The risks of further infection poisoning her body leave no option but amputation.

It is estimated that about one in three people with diabetes will develop a foot ulcer, often due to peripheral nerve damage. The loss of feeling in a “diabetic foot” can cause horrific wounds. “We’ve had patients with drawing pins and needles [in their feet],” says the unit manager, Rhiannon Joseph. One patient had “a set of keys in a shoe that he hadn’t realised he’d ended up walking on for a week”.

The unit is increasingly populated by limbless people. “There’s been a massive increase, especially over the last few years,” Joseph says. “Last week, we did six amputations [of lower limbs]; this week, we’re already scheduled to do up to three. Amputation of toes and forefoot we’re doing every day.” She estimates that 80% of patients have diabetes. Lewis points out that it’s increasingly rare for him to do lower-limb surgery on a patient without type 2 diabetes.

Nearby, David Williams, 65, from Caldicot, places his hand gingerly where his left leg used to be. “It’s painful even just to touch it,” he says. He has type 2 diabetes and this is his second amputation. Below his waist, under the blanket, protrudes the irregular outline of his stumps. Attempts were made to save his remaining leg – at one point, they tried using maggots to remove infected tissue – but to no avail. “It was absolute agony,” he says.

His discomfort is clear, but he is fortunate to be alive. Moments before his amputation, he went into cardiac arrest. He had to be resuscitated using CPR, breaking his ribs in the process, after which he developed pneumonia in intensive care. He nearly died “twice, maybe even three times”, Joseph tells me in a nearby corridor. Mortality associated with diabetes is on the rise.

“It has turned [my life] upside down – destroyed it, really,” Williams reflects quietly when asked about the impact of diabetes complications. “Not once have I sat in bed and not thought I’d rather end it all than live with no legs. If I didn’t have my granddaughter, I think I’d be gone.”

Looking back, he assumed he was taking sufficient exercise: “I thought I was getting plenty, but it was nowhere near enough. I wish I could turn the clock back, but I’ve got to live the best I can. I’ll get through it.” He lives alone and worries that he might have to crawl around his flat, until support is provided.

In a different bed, another type 2 amputee, Paul Jones, lies with one leg crossed over the other – half of it missing. He describes how a minor foot infection deteriorated so rapidly that it “rotted and hollowed out” his heel. “If you opened a tin of corned beef and scooped it out, that’s what it looked like,” he says. “I don’t think you can suffer any more pain.”

At least 8% of the adult population in Wales now has diabetes, the highest estimated rate of the UK nations (it’s 7.3%, for instance, in England), with more and more people hospitalised as a result. Wales is older and frailer as a nation, with high levels of obesity. But the rate of new diabetes registrations, mostly type 2, continues to astound.

Over the 12-year period to 2022, Public Health Wales reported an increase of almost 60,000 people with diabetes. That amounts to almost a 40% rise. “If current trends continue,” the Welsh government’s health agency warned recently, “by 2035/36 we estimate that around 1 in 11 adults will be living with diabetes in Wales.”

Amputations happen only in extreme cases. With support from charities such as Diabetes UK, many people with diabetes can manage their condition effectively. But clearly this vast diabetic caseload, fuelled in part by rising obesity levels, is stretching an already overstretched NHS. Three floors above Cardiff’s swollen vascular unit, on ward B5, there are 26 patients with kidney failure – nine of whom have diabetes. UK Renal Registry data has shown a steep rise in the demand for renal replacement therapy in recent years, with diabetes increasingly a cause of kidney failure.

Forty miles away, in Singleton hospital in Swansea, Richard sits alone by the window, waiting for his turn in the operating theatre. The 57-year-old school canteen worker can barely see the frame, let alone what is beyond it. He has diabetic retinopathy – by which, over time, excess sugar in his blood has caused an abnormal growth of blood vessels on the retina of his left eye. His vision is now obscured by bleeding from the burst vessels, so that life appears as an increasingly amorphous mass of indistinct objects.

“You’re just figures, a blur – that’s all,” he replies when asked what he can see. So much blood has leaked into his left eye that he needs an hour-long operation to extract it. “It’s fairly frightening,” he says, then adds with a note of embarrassment: “It’s zeroed my confidence in a big way.”

The Welsh government estimates 69,000 people in Wales now have some degree of diabetic retinopathy. The Singleton’s eye clinic is unrecognisable from when Gwyn Williams started working there 15 years ago. “There was no dedicated diabetic eye-injection clinic when I arrived,” says the consultant ophthalmologist. “Now, we’re filling up clinics faster than we can staff them. It’s a diabetic tsunami.”

Installed in the operating theatre, Richard is now beneath a blue drape, but still conscious. His face is covered, bar a small opening where his left eye sits illuminated, eyelids retracted, frozen with anaesthetic. We are about to witness the most intricate (and expensive) treatment for diabetic retinopathy: a vitrectomy.

Crouched over him, Mr Sidath Wijetilleka, a consultant vitreoretinal surgeon, begins his meticulous remedial work. On a large monitor, Richard’s eye appears like a full, rich orange moon, shimmering at the sides. Three tiny tubes, or “ports”, have been plugged into the white of his eye. One is used to get light into the eye, another for cutting, another to fill the eye with water to keep it from collapsing.

“This is the back of the eye,” Wijetilleka says, “and this is the blood caused by diabetes.” We examine the enlarged image. It is a vitreous haemorrhage, he explains, as he begins the process of draining the eye of the unwanted blood and diabetic “jelly”. The beeps of Richard’s heart monitor punctuate the drone of the vitrectomy machine. On the screen, we watch a needle-like suction tool move industriously around the inside of his amplified eye.

“You OK, Richard?” Wijetilleka asks. “Yep,” comes the reply from under the sheet. The theatre lights are dimmed and we are all given protective glasses. Lasering is next. Wijetilleka thinks this single operation, with staff accounted for, “probably costs about £10,000”. According to Public Health Wales, diabetes-related hospital spells cost a total of £428m in 2021/22. Drugs used to manage diabetes (nearly 4.5m items) cost the Welsh NHS £105m alone in 2022/23.

The challenges are far from unique to Wales. In June, the University of York’s Health Economics Consortium (commissioned by Diabetes UK) published research that estimated the direct costs of diabetes in 2021/22 to the NHS, UK-wide, was £10.7bn. It cited 238,000 potential years of life lost to diabetes, along with nearly 12m sickness absence days in just one year.

There is a tiny, near-windowless office at the end of a corridor in Singleton hospital’s eye clinic. On Sue Neale’s desk are pamphlets from the Royal National Institute of Blind People (RNIB) headlined “Worried about your vision? I’m here for you.” She is one of the RNIB’s eye care liaison officers. Many of those she helps are living with diabetes.

“I get a lot more patients now with diabetes who are still of a working age and need support to see how they can retain employment,” she says. “It’s a double whammy, requiring practical support and emotional support, too.” She helped one woman, a single parent with two children under the age of five, who lost her sight because of diabetes: “It is devastating to see someone so young have to deal with a new way of life.”

The cruel effects diabetes can have are compounded by the injustices involved. People from Black African, African-Caribbean and South Asian backgrounds, for instance, are at risk of developing type 2 diabetes from a much earlier age than white people. Type 2 diabetes is also markedly more prevalent in areas of higher deprivation. You need only to wander along a high street in a south Wales valleys town, for instance – peppered with fast food outlets – to understand how diabetes thrives in such obesogenic environments. Inequality is the backdrop to this crisis.

When the medical journal The Lancet noted recently that 1.3 billion people worldwide could be living with diabetes by 2050, it said: “In every country, those who are discriminated against and marginalised suffer the most and worst consequences of diabetes.” It called diabetes “a defining disease of the 21st century”.

Prof Devi Sridhar, a public health expert at the University of Edinburgh and Guardian columnist, recently described the former UK government’s approach to health policies as one of “false economies”. Like others, she believes too little is being invested in anti-obesity strategies and supporting those from less advantaged areas to access affordable, nutritious foods.

As a result, she wrote, “the NHS has to spend more on acute and chronic care for those developing diabetes and needing treatment and support”. Diabetes-related coronary heart disease, for instance, cost the NHS an estimated £1.5bn in 2021/22, according to the York Health Economics Consortium.

Across the UK, various national diabetes prevention programmes have been established. In Wales, the devolved government has been pushing ahead with its diabetic eye screening programme. It is rolling out intervention work through GP surgeries for patients who are considered to be pre-diabetic. In Cardiff, the health board has established new models of care, with emergency diabetic foot clinics. New laws are being enacted in Wales to restrict the promotion of products high in fat, sugar and salt in certain stores (similar legislation has been delayed in England). NHS England has this week announced promising results of a trial of its new “soup and shake” diet. For one in three who completed the year-long programme, their type 2 diabetes went into remission. But, across the UK, the public health challenges involving diabetes remain vast.

Meanwhile, the obesity epidemic shows no signs of abating. The National Survey for Wales estimates that 62% of over-16s in Wales are overweight or obese. According to the chief medical officer for Wales, nearly one in three children are overweight or obese by the time they start primary school.

In the operating theatre in Cardiff, Lewis and his team have been threading stitches around Watkins’ newly formed stump. As we leave, I ask him about the projection that, on current trends, there could be nearly 50,000 more patients in Wales with diabetes in just over a decade. “The NHS is always very good at coping,” he says, “but it’s going to be a big ask, isn’t it?”

And with that, another operating team begins to arrive, waiting for their next slot. Knife to skin. It is relentless.

Andy Davies is Wales and west of England correspondent for Channel 4 News. His film On the Frontline of the Battle Against Diabetes in Wales is available on channel4.com and YouTube

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