I would dearly love to know what they are including to get an average UK spend of $629. From a brief scan of sources and data set they don't appear break it down any further.

More in the UK get free prescriptions than don't. Even with the most involved care I can't find a way to make it that expensive. So maybe they're including people voluntarily paying some treatment not available on the NHS like homeopathy or unproven experimental treatments, or private insurance generally. Maybe they count dentistry as healthcare.

Prescription charges for some, hospital parking, drinks machine... Unless you include something else it doesn't add up.