Relatively few countries have that rule - the US and Canada are the two best known countries.
In general, I wouldn't sweat it on Brexit with passports (I too have an EU and a British/ soon to be non-EU passport). Either it will all be fine and there's nothing to worry about, or it will be a disaster and so you entering the UK on an EU passport is going to be the least of anyone's worries. Based on yesterday's announcement they won't bother checking trucks coming into Dover maybe they'll just get rid of immigration for a while. At least "we'll have control of our borders"
