Mushy, I'm sorry, I did not mean to be patronising, I was just impressed by Kurnals's dedication.
However, to return to the question, you need to look at the interpretation of domestic premises;
"domestic premises" means premises occupied as a private dwelling (including any garden, yard, garage, outhouse, or other appurtenance of such premises which is not used in common by the occupants of more than one such dwelling);
clearly the stairs etc are used 'in common' and therefore fall under the Fire Safety Order.
The responsible person, other than in a workplace, is best thought of as the person who has, or exercises 'control'. In your case this could be a company if the residents have set one up to manage any maintenance or they may have apppointed contracturally a manageing agent to look after the fabric of the building, more likely the occupants would be deemed jointly and severally, the responsible persons. In theory if there was a breach, all of them could stand in the dock. This is extremely unlikely to happen but is technically possible.
Hope this helps.