If I have understood correctly, you need to travel on your British passport to avoid having to get an ETA OR get a certificate of entitlement (which costs £550!!!) This seems very unfair to me and is particularly so for those of us who have dual nationality kids who want to travel home to see grandparents.
My kids actually do have UK passports now but did not get them for a long time as we are a relatively low income household and getting everyone two passports when not really needed was too much. I think a lot of people are going to be caught out this way! Oh for the pre-Brexit days when you could travel on a £15 ID card....
Anyway, is this right? Has anyone been turned back because they are a British citizen but without a passport?