Bit of a misunderstanding here I think. It's the actual index they look at, not the % change in the index over the last x months that the papers report as the RPI. If the RPI falls, that means we have (in theory) actual deflation, so you get the benefit of all your money back + 0.5% + everything got cheaper while you were waiting.
NS&I - Index linked savings certificates
NS&I - Index linked savings certificates
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