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find a broker that deals with business proprietors / self employed, as a 302 is a fucking pita for finance. a good broker will have arrangements with the lenders for various finance/mortgages, such as > http://www.buildstore.co.uk/finance/self-build-mortgage-types-comparison.html <, and will be more interested in your recent accounts, plus business case and projections for the next 4 years
You probably wont get a resi mortgage because of a combination of your work situation, the structural stuff and the lack of kitchen.
But with a 50% deposit you could look at development finance. Find a mortgage broker that knows such things.