A registered office is, in effect, just an adress where CHouse, HMRC etc send official company mail.
Also, working from home.. as millions of people now do, doesn't constitute running a business from home.
This is also true if you're working from home, as the sole employee, of a company of which you're the sole director who's registered adress is your home adress.
Your landlord may, quite rightly, have concerns that if you go tits up, owing loads of money, people may start turning up at the property and harrassing his next tennants. Which is fair enough, I just wouldn't have told him.
I'd love to see those property ads in the paper... NO SMOKERS, NO PETS, NO DSS, NO COMPANY DIRECTORS....