Which she did. A family member eventually paid for her to have private treatment and she was diagnosed with atypical anorexia – all the symptoms but not the right weight.

But what is the right weight?

Prof Tim Kendall, England’s most senior mental health adviser, says weight shouldn’t come into it.

”If you leave an eating disorder until it’s got to the point where, say with anorexia, they’ve lost say a third of their body weight, that has a lot of longer-term outcomes which make it very difficult to treat, so it’s wrong in my view to leave this until it’s get very bad.

Prof Kendall believes patient choice is important and community care has a much better opportunity of success. It should never be withdrawn, he says, and hospital treatment should be enforced only in the most extreme cases.

Guidelines from the National Institute for Health and Care Excellence( NICE) state that on its own, BMI is an unreliable measure of an eating disorder.

BBC Breakfast asked all 62 mental health trusts in England and Wales if they used BMI to decide who would qualify for outpatient eating disorder services.

Image caption Claire’s BMI was too low to qualify for outpatient care

Of the 44 trusts which answered, one-third said they did.

Most said they used it along with other indicators – such as the speed of weight loss. Four trusts, however, said it was a primary measure. They were Derbyshire, Cumbria, Coventry and Kent and Medway.

In some areas, patients might be refused access to services if their BMI was over 14. In others, like Kent and Medway, if it was over 17.5.

Some trusts said they had a minimum threshold under which people might be refused outpatient services.

This is what happened to Claire: ”The first thing they did was weigh me and tell me my BMI was too low.

“I would have to go to hospital. I didn’t want to, I’d had a bad experience before and I thought I was making good progress as an outpatient. So I was left to my own devices.

“Everyone’s eating-disorder experience is completely different, you can’t set everybody in the same box – you have to listen to the person, to how they are feeling.”

Image caption Sarah Hodge said resources were limited

Sarah Hodge, from Kent and Medway Partnership Trust eating disorder service, said they would rather not use it as a measure at all, but the problem was resources.

The Department of Health says more funding is on the way: “We are expending 150 m to develop community service in every region of the country for children and young people.” Eating disorder guidelines from NICE are being redrafted. The hope is some of these concerns will be addressed when new guidelines are published afterwards in the year.”

Eliza said: ”You wouldn’t tell person with cancer to come back when their condition had degenerated, why tell person with an eating disorder? “