Thanks Superman, that link confirms that the Consumer Price Index does indeed take mortgage interest payments in to account.
Next question
How is the Consumer Price Index related to the rate of inflation that we hear about in the news (currently around 4% I think) or are they one and the same?
yes the DoF MEB keeps a nice section on inflation. Afaik, the HICP measure of inflation, as against the CPI (it's the harmonised european measure) doesn't take into account interest rate increases, so that's why CPI tends to be higher than HICP in Ireland's case.