The wedge between the UK retail price index (RPI) and the consumer price index (CPI) widened to 3.3 percentage points in November, the highest it has been since records began in 1989. Typically, the RPI overstates inflation, for several reasons: because it uses different methods of aggregation, its choice of which items are included and the weights it attaches to those items. The widening gap is most probably a result of the rise in mortgage interest payments, an item that the RPI measure includes while the CPI does not. Mortgage interest payments were up 32.3% on the previous year in