I suspect that regular check-ups for most people would simply regularly confirm what they already know: they need to lose weight, stop smoking, take more exercise, eat more fruit and veg.
The UK now has a sugar tax on soft drinks that seems to be having a measurable positive effect. Whether it is a meaningful effect remains to be seen though:
"The findings suggest that a year after the sugar tax was introduced, adults reduced their daily free sugar intake by about 10.9g, and a reduction in soft drinks accounted for over half of this reduction. This translates to a reduction of around 40 calories daily, which if maintained, and assuming no other changes, could lead to 1.5kg weight loss over a year."
https://theconversation.com/how-do-we-know-the-uks-sugar-tax...
So perhaps instead of exhorting people to do better the state should continue to try to make bad habits more expensive and good habits cheaper.
Yes a regular check-up wouldn't be the silver bullet but it would help expose larger problems under the surface which could be prevented with prescribed exercise, diet, etc.
Ultimately it's down to the patient to put in the work but if the NHS focused more on creating community practices where these things could be more widely available then maybe we should see more meaningful change.