Each missed NHS hospital appointment costs the NHS around £160. A fine for failure to attend should help cut this. Non-attenders inflate waiting times considerably. I suggest £10 for a missed GP appointment, £50 for a hospital appointment and £150 if you miss an operation without good reason.
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A reminder letter should be sent 2 weeks before the appointment, followed up by a phone call to confirm attendance. A list of those who can come at short notice could be kept in case of cancellations.