AFTER 25 years of waiting, many of them in overcrowded tenement flats with three children, Betty Waddell finally moved into a home with a front and back door exactly three years ago.

Now she faces having to move out again if she can't find £85 a month from her disability benefits when the spare bedroom tax kicks in.

"I was overcrowded for years, but I never got compensation for it. But now I'm being penalised for being under-occupied," she says.

Like an estimated 18,400 social tenants around Scotland, Betty has two more bedrooms than she needs for herself – on paper at least.

But the property, supplied by Calvay Housing Association in Glasgow, is more than a box to be measured only in square feet.

It anchors and shelters a large, often vulnerable family in ways the benefit reforms are blind to.

A grafter from 15 to 45, Betty has been off work for seven years through a mix of disabilities, including osteoarthritis in a hip that needs a new joint, chronic sciatica, and cervical spondylosis.

The latter two won't heal, but once the hip is fixed, she hopes to get back to one of her old jobs working in a cafe or as a cleaner.

Forced to walk with a stick, Betty often has a carer stay overnight, but because it is not seven-day care, the sleep-over room is regarded as surplus.

The other "spare" room is needed for her eldest daughter, who suffers from bipolar disorder, and has attempted suicide more than a dozen times.

When her condition approaches a crisis, or when she is just out of hospital, it is Betty's house she turns to, while Betty's 15-year-old grandson uses the room when his mother is unwell.

If the room wasn't there, Betty fears the worst.

"It is not feasible for me to downsize because I'm not putting my child's life in danger," she says.

Government advice for tenants like Betty is to work more or move somewhere smaller, but Calvay doesn't have smaller properties to spare.

The association's stock was tailored to meet local need – and that meant houses for families. Many of those families will now lose 14% or 25% of their housing benefit because their children have moved out, leaving them "under-occupied".

The Scottish Government says such empty-nesters are the largest group affected by the change.

Because she wants to stay in the home she waited so long to get, Betty says she will have to spend less from April, both on essentials such as gas and electricity, and on treats for her grandchildren.

By ignoring the complexity of family life, she fears the bedroom tax will not only scythe through her community but will also have an impact on scores of others if it is not stopped.

Betty said: "It is a basic human right to be with your family, to be there for them. David Cameron says he's all for the family, but this is breaking up the fabric of family life, and breaking up communities.

"We are talking about utter chaos."