The original advert had said that the flatmates "like to chill out a lot together" so they were '"not really looking for somebody that just wants to stay in their room".
Last night landlord Dan Smith, who is charging $140 a month on top for bills, had not responded to inquiries about the cupboard - so was unable to clarify whether there had actually been a previous tenant who enjoyed "staying in their room/cupboard".
While Mr Smith was not available to discuss his under-stairs space, it stirred up a storm of controversy on the internet after Miss Lomax, 23, tweeted pictures of the miniature lodgings.
Miss Lomax, a journalism graduate, posted the above on Twitter referencing Privet Drive - the street where Harry Potter lived in a cupboard under the stairs with his uncle and aunt.
Speaking about her flat viewing in Clapham, south London, Miss Lomax said later: "My first reaction was shock to be honest. I wish I'd been angrier at him, because I left fairly quickly and politely saying it just wasn't for me.
"He showed me the room pretty much straight away, so I didn't get to see much of the house itself. I think he said it was three or four others staying there."
Miss Lomax, who has been looking for a flat for a month, said landlord Mr Smith seemed "nice enough", but was unapologetic about trying to rent out the cupboard.
Miss Lomax, a recent university graduate, said: "I don't know much about the housing market, the other places I've seen haven't been right for me but certainly nothing wrong with them."
Miss Lomax's post on Twitter had last night been shared several thousand times - and been greeted with widespread condemnation.
A spokesman for housing and homeless charity Shelter said: 'Blimey, not another one. We'd love to say we were surprised... however we cannot."
- Daily Mail