I asked the home office what it would take for me to stay. Note that this was in 2018, so some time before they'd actually nailed anything down formally. Anyway they told me I'd have to apply for indefinite leave to remain, and eventually become a Brit. There was a fee too, I think ~ £1000. And the kicker, they said I was only allowed a UK passport and one other. And so I left the UK.

Having left I no longer paid much attention - I have no idea what the actual rules/requirements are for EU citizens with an additional non-EU citizenship to naturalise into the UK. And honestly I was so destroyed by the referendum anyway that I doubt anything would've kept me in the UK. Crazy sad.