I am a South African citizen living in the UK 22 years with indefinite leave to remain.
Do I need Schengen travel insurance to go to Portugal if I'm covered by the NHS in the UK?
Yes, as the NHS does not provide coverage that is required as part of the Schengen insurance (even with the EHIC). Specifically, Schengen insurance covers:
EHIC has this disclaimer:
Note: The EHIC is not an alternative to travel insurance and will not cover any private medical healthcare or costs, such as mountain rescue in ski resorts, being flown back to the UK, or lost or stolen property. The EHIC will also not cover your medical expenses if you are going abroad specifically to have treatment.
In any instance of travelling it is always recommended to have a valid travel insurance policy, but there is nothing to say that you have to. In the event of anything happening you will simply not be covered for that incident and you will have to pay the full amount of health cover.
However the European Health Insurance Card gets you free or discounted treatment in state run medical practices in the EU and other countries. Which basically entitles you to the same level of cover as a local of the country you are in would expect.
To get cover in the EU (Including Portugal for your example) and other countires/teritories you need a valid European Health Insurance Card which is free, but does not replace travel insurance. It entitles the holder to free or discounted medical treatment at state-run hospitals and GPs in any European Union country, plus Iceland, Liechtenstein, Norway and Switzerland. It replaced the old E111 form in 2005.
As a UK resident and not a EU/Switzerland citizen you can apply by post with proof of address and proof of residency (visa, HO letter, employer letter or approved forms).
Beware of fake EHIC websites. There are a few out there. Always use the official site ehic.org.uk