Yeah, well I don't know what to say, really -- keep trying! Are you British? It's always good to have connections, or be good looking, if you are trying to get a novel published in the UK. If not, have some kind of interesting life story to hang the title on -- like being a bus driver, or something. If you have none of these things, and don't emerge from the elite educational establishment, the only way around it is to be outstandingly talented, either in an acceptable, staid way or in an extravegant, Gallic, outre way, though the latter route is more difficult, admittedly.
Or, Network, Network, Network, as we used to say in the Labour party -- bombard little magazines and online magazines and literary journals and competitions with snappy short pieces, stories and sketches and reviews, and generally hobnob with the literati underground, make your name known within the small circles and it will slowly filter up, or fester. At the very least -- assuming you get stuff published or printed -- you will have a small resume of bylines and allies to garnish your novel submissions. You will have made a name for yourself, found a niche. The aformentioned Owen Hatherly is the model to follow in some ways, but apply the same logic to fiction; harder to do, I am sure, but still possible.
In the meantime, you will have had practice writing, and worked on the novel some more, maybe, changed bits around, perhaps -- unless you consider it totally polished and finished? It's not unsual to get hundreds of rejection letters, but sometimes the difference between a book deal and oblivion may just be one crucial rewrite, edit or insertion, so with every round of rejection letters, I would consider it to be a lucky chance to rework the work, work out what's missing or what should be missing, and work and work and work. (Cut, cut, cut some more, I always say, like George Oppen.)
Publishers like to perpuate the myth that they actually sit around reading manuscripts and occassionally get smacked in the face by An Outstanding Work, when they actually go on CV, publicity photo, covering letter, connections and opening chapter. Depending on how much confidence you have in your book, and how successful you want it to be, you have the construct the package. There's not a lot of money or guts going around in publishing, they're all scared little cynics, scarred Eng. Lit. Grads struggling to stay alive in the world of retail and business, with monsters and aliens roaming around, feared CEOs from other sectors, restructuring and setting targets and sacking them and things. You have to sell yourself to them, because they have to sell you; they have tight targets to meet.
Unless you're pulling some Plum Sykes or Alan Titmarsh stunt, this could conceivably improve your work. Don't dismiss the rigorous, if unpalatable, aesthetic benefits of the market!
(I was only joking about Plum Sykes. I love Plum Sykes.)