Many people may be suffering from an undiagnosed and misunderstood bowel condition, according to the charity Guts UK.

Microscopic colitis is an inflammation of the large bowel and causes frequent watery diarrhoea, stomach pain, faecal incontinence, fatigue and weight loss.

About 17,000 people are diagnosed each year in the UK, but experts say the real number is likely to be higher.

Some standard tests for inflammatory bowel conditions do not spot it.

But despite misdiagnoses, cases have risen in the UK in recent years.

Victoria Rennison, 33, from South London, was diagnosed with microscopic colitis last year, after more than a decade of symptoms.

She saw a number of specialists but was told she had irritable bowel syndrome and “was left to get on with it”.

When the condition was at its worst she would spend the entire day and many nights on the toilet, or running urgently to the bathroom.

“The diarrhoea would come on suddenly and would be profuse and watery and the pain was like intense cramps,” said Victoria.

“There were even times my infant son had to sit on a bouncer in the bathroom with me for hours.”

She told BBC News: “I used to be sociable and outgoing but I found it harder and harder to go out.

“I didn’t want to leave the house. I had to make a map of every toilet to do so.”

Victoria was finally diagnosed after a gut specialist did a colonoscopy (camera test of her bowel) and – crucially – took biopsy samples of the inflamed bowel.

On previous visits to doctors she had had colonoscopies, but no biopsy samples had been taken and the condition – which can be seen clearly when samples are put under a microscope – was missed.

She says it was a huge relief to get a diagnosis and be given treatment.

“It was not possible to keep living like that with a small child. I feel like I’ve finally regained some semblance of normality.”

Julie Harrington, CEO of Guts UK, said it was crucial to provide training for healthcare providers, and continue to raise awareness, and invest in research.

She added: “It is terribly sad that thousands of people are suffering with the debilitating symptoms of microscopic colitis.

“Most people with the condition can be easily treated with a course of gut-specific steroids or with symptom-relieving medicines, but getting a diagnosis is the first, essential step.”

Prof Chris Probert, at the University of Liverpool, said: “It is not clear why cases of the condition are on the increase, but it is likely to be due to a mixture of increased awareness of symptoms leading to more diagnoses, and environmental factors.

“The good news is that effective treatments are available, so people experiencing symptoms could benefit enormously by talking with their GP.”