Don't go cap in hand, you're offering to make him money, he isn't doing this out of the goodness of his heart, he's offering to give you £20,000 in exchange for £35,000 and if it turns out that you haven't got the £35,000 he can have your house.
The Alpi looks quite nice, you could ask the bank manager for twice as much and build me one, if you like. I'd ask my own bank manager but I've just done it (twice) to buy all sorts of stuff that I never mentioned to him.