Many policies of all types may suggest they have worldwide cover, but that is almost always only for emergency medical treatment- it does not cover you for choosing to go overseas for treatment.
The vast majority of private medical insurance policies do not allow treatment outside the UK.
The handful of private medical insurances that do allow treatment outside the UK, rarely cover dental, cosmetic or lots of other treatments that people go overseas for.
Most travel insurance policies now have exclusions on going overseas for treatment.
Medical negligence policies only cover hospitals not the customer, but a special new policy has been launched.
International insurance policies are designed for people who are expatriates -those working or living outside the UK, not for UK residents.
International insurance policies only provide very limited cover for travelling between countries for treatment.
Cost over-run policies are available, but rare; and many are just uninsured guarantees.
Very few dental insurance policies cover non-emergency treatment outside the UK.
Policies will not pay your travel costs
There are as yet few special policies designed for the medical traveler.
If you are thinking of overseas treatment this is often for an existing problem you have. Insurance policies exclude pre-existing conditions and existing problems.
Many people are tempted to avoid the problem by lying/ failing to disclose that the whole or partial purpose of a trip is for treatment. Failure to reveal relevant information can invalidate the policy rendering it worthless. Failure to reveal the true purpose of a trip when making a claim, is fraud, a criminal offence.