Extraordinary monetary policy and the latest extension of its money-printing bond-buying programme could have taken the Bank of England's real interest rate to as low as minus 2.5 per cent.
Fresh analysis by investment outfit Hermes has found that adjusting for the impact of quantitative easing on "true" central bank rates, the UK and the US are effectively running their own negative interest rates.
The calculations are based on internal figures from central banks around the world which have quantified the scope of quantitative easing and its relationship with interest rates.
The Bank of England, for instance, estimated that £200bn of bond-buying is the same as a 1.5 percentage point cut to interest rates. The US Federal Reserve, meanwhile, estimated pumping $600bn of fresh money into the world's largest economy was the same as a 0.75 percentage point cut.
The Bank of England's official interest rates are currently 0.25 per cent, the lowest in its 322-year history. The US Federal Reserve is currently operating a "target range" for interest rates, which is set between 0.25 and 0.5 per cent.
Combining the banks' internal calculations with their current headline rates and the size of their quantitative easing packages suggests the "real" interest rate in the UK is minus 2.5 per cent, while in the US it could be as low as minus 4.5 per cent.
Neil Williams, chief economist at Hermes said he was worried about central bank's "increasing addiction to quantitative easing [which] offers little to push productivity and wages, still the missing piece from most recoveries."
He added that he believes the US will "fail" in its fledgling attempt to put monetary policy back on a more normal footing, with headline interest rates rising to just one per cent during this particular cycle.