I think the first bank who devises a method of transferring funds that requires both parties involved's authorisation to change would make a killing. It doesn't have to cost anything - just the number of customers who would want to set up an account with them.
Imagine it - yes, I'll lend you £500 but we're going to set up a guaranteed payment thing: If we don't both cancel it in 6 months time, your bank pays me £50 quid a month out of your account into mine automatically (by standing order, direct debit, etc) until the debt is paid off (or plus interest).
Of course, there are banks and other companies around that will give you loans, and they simply won't lend to unreliable people - that's people without incomes and people who have bad credit history. That's the way the industry has evolved, and it's done so for a reason...
But it would fill a niche in the market, the 'friends loan'...