From the BBC:
The NHS says it has saved millions of pounds in the last year because of the number of patients failing to turn up for appointments.
It is estimated that more than 12 million doctors' appointments are missed and just under seven million outpatient hospital appointments are missed each year.
Although there is an administrative cost associated with each appointment, the NHS does not incur any further costs in treating patients who do not turn up.
On average, a GP or consultant gains twenty minutes from each missed appointment which can then be spent with other patients.