National sources of advice / representation?

Over the past year or so, I've seen numerous suggestions on various forums suggesting that people turn to their local "advice centre" or similar words for help with their benefits claims, but it's actually a very hit-and-miss thing to Google on.  Not only because the amount of resources available varies so much across the country, but also because optimising your search terms is incredibly difficult.  I wondered if there is actually an extensive list somewhere of people/organisations who can help with this?

If not, I'd start by suggesting:

- Citizens' Advice Bureau

- local council Welfare Rights Officer

- charities related to whatever conditions you have

- https://www.adviceuk.org.uk/

- https://www.turn2us.org.uk/