Nearly 98 per cent of people will survive bowel cancer if it's detected at stage 1, a figure that drops to 10 per cent if diagnosed at stage 4.

Awareness campaigns, plus the NHS screening programmes for people aged 55 and 60-plus, mean generally, the prognosis has improved for older age groups, those most likely to get the disease (around 94 per cent of the 41,200 people diagnosed with bowel cancer every year in the UK are over-50s).

But the number of younger people with bowel cancer has increased by 45 per cent since 2004. There are currently more than 2,500 new cases a year in the UK in under-50s – and they are much more likely to be diagnosed late.

According to Bowel Cancer UK, three out of five will be diagnosed with cancer that's already stage 3 or 4. A third (34 per cent) only find out they have cancer in an emergency situation, after having to visit A&E, for instance, because symptoms have reached a crisis point – despite the fact they may have been seen a doctor numerous times.

Mark and Beth Lyson recall how their daughter Hannah – the 20-year-old who amassed thousands of followers when she blogged about fighting bowel cancer, before passing away in January this year – was "back and forth to the doctor" for years.

At first diagnosed with an inflamed gut, later in 2013, her GP said she probably had irritable bowel syndrome [IBS], the common, benign condition associated with a range of digestive symptoms. Hannah was prescribed medications to help with chronic constipation and worsening back pain, but no tests were carried out.

"The main thing she went back with was her back, she was always complaining about her back," says Beth, 55. "Then in August 2015, she went to Florida with her boyfriend and was sick a few times. We thought perhaps it was something she was eating, because of the doctor saying it was irritable bowel."

But the vomiting continued, on and off. "She'd be sick for a day, then she'd go a couple of weeks and be fine, then she'd be sick again," says Beth.

Mark, 52, recalls encouraging Hannah to return to the doctor, but "she was saying, 'Well it's a waste of time going because they don't do anything'."

The tipping point came when summer 2016 approached. "Hannah was due to go to Camp America last June, and we were getting frightened that she couldn't go, she was in that much pain," explains Mark.

Beth took Hannah to see an on-call GP, and pleaded that tests be done to make sure she was well enough for her trip to the US.

All they wanted was reassurance it was safe to allow their daughter to jet off to America. But two weeks later, in May 2016, Beth and Mark found out that their sporty, Disney-loving 19-year-old girl, who didn't drink, didn't smoke – didn't fit any of the at-risk categories - had a tumour in her bowel, and four tumours in her liver.

"She already had her case packed for America, she was that organised," recalls Mark. "She had her T-shirts, shorts, flip-flops and all these things. The case was in the conservatory with name tags on it... It was devastating."

Even the doctors were shocked, saying it was the youngest case they'd ever seen. And it was shocking, but looking back, Beth and Mark, from Burscough, Lancashire, can see that opportunities to discover the cancer sooner were missed.

"Bowel cancer in younger patients is becoming more common; we don't really know why," says Willie Hamilton, professor of primary care diagnostics at the University of Exeter Medical School.

What he and his colleagues – who have teamed up with Bowel Cancer UK's Never Too Young Campaign, Durham University and University Hospital of North Tees – are certain of, is that more can be done to ensure young people with bowel cancer get diagnosed as early as possible.

Based on research, they're launching a new risk assessment tool, published in the British Journal Of General Practice and funded by the Department of Health, designed to help GPs identify when symptoms in the under-50s might indicate a serious bowel condition, including cancer or inflammatory bowel diseases like Crohn's, as opposed to more common conditions like IBS.

A scoring system will indicate whether the GP should simply monitor how the symptoms progress, recommend tests such as checking stool samples for signs of inflammation, or refer somebody for an urgent colonoscopy or to a specialist.

"The key thing is we now have a much stronger idea which patients with bowel symptoms might have an unpleasant disease - like cancer. We know which symptoms, like rectal bleeding or diarrhoea, should be tested, and what test to use," says Hamilton.

Systems like this level out the playing field too, as often symptoms can be vague, plus the severity of symptoms doesn't always reflect the seriousness of the underlying cause.

For Dave Smale, 36, who was diagnosed with stage 4 bowel cancer this January, the only symptom was stomach pain. "He started getting stomach pains, which correlated with when he'd been eating," explains his wife Katie, 31. "We later found out this was because everything was trying to come past the tumour in his bowel, it was obstructing everything. But at the time, we were racking our brains about what it could be. We thought perhaps it could be a food intolerance, or IBS."

That's what Dave's GP thought too at first. But a few months on, the pain became severe, and Dave was referred for tests. He was told he could be facing a diagnosis of Crohn's disease, but the results were far worse - cancer, that had spread to his liver and stomach lining.

Dave's already had major bowel surgery and is currently undergoing chemo, with more surgeries to come. Life's been turned upside down for the couple, but their 15-month-old daughter, Maisie, is keeping them laughing and little things, like pre-chemo date nights, plus support from family and friends is helping.

Katie's grateful Dave persisted with going back to the doctor, and says "I think he'd started Googling about how people had been misdiagnosed with IBS and it turned out to be something worse".

Of course, "IBS is real, common and troublesome", stresses Professor Hamilton. "We need to identify bowel cancer as early as we can, but we do have to remember most patients with bowel symptoms do not have cancer. GPs have always had to do a delicate balancing act between testing too few patients and testing too many.

"Most patients can be managed entirely within their GP's surgery, but some will benefit from tests of their faeces, and a few will need an urgent colonoscopy."

In the eight months Hannah fought bowel cancer, she managed to inspire thousands, and help fundraise, through her positive blog posts.

"No parent should have to go through what we went through," says Beth. "When it's caught early, you can save somebody's life. People need to wake up.

"Even when she was really poorly, Hannah always wanted to keep positive, she's always been like that, she wanted to raise awareness with her blogs and videos. That's why we're supporting the Bowel Cancer UK's Never Too Young campaign. It's what Hannah would have wanted. "

For more information about bowel cancer, visit bowelcanceruk.org.uk