Hello… 
I’ve been summoned!
I’m the person who managed to (eventually) get my address showing on Monzo. You’re right, I never mentioned in the original thread exactly how I did it. Back when I was trying to figure this out, I asked Monzo’s support team outright who provided the addresses, and they refused to tell me, so they obviously have their reason.
I didn’t want to disclose it on Monzo’s own forum, and risk inviting the wrath of the powers–that–be — so forgive me for being slightly cryptic!
But here are some clues to help you out…
- Your address must be listed with Royal Mail as a prerequisite — but, this is not where Monzo’s address lookup sources the data from.
- Once your address is showing up with Royal Mail — in a totally unrelated matter — go and check your free credit score with the Big 3 credit rating agencies.
- Maybe try and register with each one in alphabetical order? (No particular reason… Honest…
) - You may (or may not) find that the address lookup on the first one’s registration screen is also unable to find your home address. Funny, that.
- If that’s the case, phone them up and request your address is added. Wait 4-6 weeks, then try and check your credit score again. You should be able to sign up this time. Congratulations on completing this entirely irrelevant side-quest!
- Come back to Monzo and try and register. You never know, maybe something might have magically changed in the interim. Who knows.
(Note that I signed up for Monzo about 9 months ago. They may, possibly, have changed provider since then, but based on comments here it doesn’t look like it.)
Have fun!