When registering for a doctor or something, you generally just tell them where you live and your name. You might also need your national insurance number. If they want more, its usually a utility bill proving that, or if they want photo ID, a Driving Licence or Passport, if you have one.
For things like voting, you don't need any ID at all on the mainland.
For things like voting, you don't need any ID at all on the mainland.