Harford and Ferguson on microfinance

Tim Harford in the FT:

if microfinance institutions can find ways to provide savings accounts to the very poor - despite sceptical regulators, a difficult business environment and tiny transactions - they will not need much of the foreign capital commercialisation is supposed to provide. Most poor households are savers, or would like to be. Many poor countries are savers. All that is needed to raise the capital for making fresh microcredit loans is a successful deposit-taking bank for the poor.

I've been watching Niall Ferguson's "The Ascent of Money" via on demand, and am impressed - even considering switching the order of my "macroeconomics and fiscal policy" and "monetary policy and fluctuations" lectures to factor in the historical emergence of banking. In it he goes through the books of a loan shark in Glasgow, highlighting someone that was lent £10 and expected to pay back £12.50 at the end of the week. This example is crucial for understanding microfinance, where aversion to high interest rates often prevent outsiders from supporting such institutions. This seemingly manageable debt constitutes an interest rate of 25% per week, or 11,000,000% per year.
Finally, why is it that scousers ask to "lend a fiver"?