As a dual citizen living outside the UK, to visit Britain I cannot apply for an ETA. Instead I must have a British passport, OR apply for a waiver document for an eye watering £500.
Obviously this makes no sense, because if the ETA is suitable for a non-British citizen it ought to be fine for a British citizen who happens to have a non-British passport, but objections have all received non-answer-answers that strongly suggest the bureaucrats didn't think of it and can't be bothered to implement support for the situation.
I hate paperwork...