Interest rates up 0.9% but premium bonds don't move

[Alaric]

I have never understood what the difference is in terms of coverage between the two indices (I should access the ONS website) but it makes a substantial difference in terms of income.

There's a difference in method. The RPI works much the same way as a stock market index such as the FTSE 100. You take a basket of goods and measure the price changes. The CPI uses an averaging process. Essentially it implies that if, say, steak, increases in price, you substitute chicken.

The lesson of the National Savings Certificates for the Government would be that Indexed borrowing can be expensive. That may well be why they discontinued those certificates. The parallel Indexed Gilts can be priced so that their return doesn't match either inflation measure.

[dealtn]

The parallel Indexed Gilts can be priced so that their return doesn't match either inflation measure.

To be clear that pricing is determined by both issuer and buyer in combination, in other words "the market". The Government doesn't have the ability to set that non inflation matching issue price.