According to a recent government decision, all foreign nationals will automatically be covered by health insurance upon entering Iran.
Foreign nationals holding health insurance from their countries of origin will not have to apply for medical insurance in Iran, provided their home country health insurance is acceptable to Iran's insurance companies.
The Iranian Foreign Ministry or Interior Ministry should introduce foreign nationals in need of medical services to one of Iran's health insurance companies.
The only difference between health insurance coverage for foreign nationals and Iranians is that foreigners will pay all insurance premiums on their own.
This is likely to make some people travelling to Iran or going to work there think that they no longer need insurance. This would be very wrong.
If you want to lie in hospital while an Iranian insurer tries to work out if the NHS is an acceptable insurer, which might take some time, as the NHS is not an insurance company, then take the risk.
If you are going to Iran on holiday or business buy travel insurance.
If you are going to Iran to work there, buy international health insurance as that will not only pay for treatment there but also provide emergency evacuation to the UK.