The increase, described by Boris Johnson as "balanced", is 1% above the Retail Price Index (RPI) measure of inflation.

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The increase, described by London Mayor Boris Johnson as "balanced", is 1% above the Retail Price Index (RPI) measure of inflation.

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The CPI was a more "appropriate" measure for changes in the cost of living of pensioners and benefit recipients than the retail price index (RPI), he said.

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In the U.K., index-linked gilts adjust for movements in the Retail Price Index (RPI) and are similar to their American cousins, Treasury Inflation Protected Securities (TIPS), which track the Consumer Price Index (CPI).

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The condition to peg off-peak fares at RPI -1, or 1% below the retail price index measure of inflation, will be written into the contract for the next rail franchise.

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