From widening spreads on many countries' sovereign bonds to Britain's failure to sell all thegilts it wanted to at a recent auction, there are signs that stimulus has its limits for some.
The government could have a one-off tax increase, two years later, to get back the money that has been paid out, just the Bank can now sell back thegilts it has bought under QE.
For Prof Miles, this raises an obvious question: what, exactly, do we get out of a "helicopter drop" - or the bank just extinguishing all thegilts it has bought - which we do not get out of the policy we have now?