Here's the rub.
I've got a mate who's a radiographer (head of dept in a teaching hospital) who says of "bad backs":
"...although to be fair it's VERY hard to tell when someone is 'swinging the lead'. Most GPs order a quadrant series of x-rays of the affected area, but that'll only tell us anything IF there's physical wear and tear to bone or cartilage OR if we're lucky enough to be able to visually detect stuff like bone spur growths. Unless you do an MRI you just can't get anything near a full picture of cause, even if the patient is reporting all the symptoms that indicate a particular diagnosis. Our problem is that while GPs will authorise x-rays (less than £50 for a series at our trust), they won't authorise MRIs (anything from £200 up to £1,000). Catch 22"
That's a direct C & P from an e-mail, written by a professional who despairs at the fact that "bad back" isn't taken properly seriously, and that many people don't get referred for MRIs rather than x-rays until damage is so bad it isn't treatable.