In addition, the Retail Prices Index (RPI) measure, which includes mortgage interest payments, rose to 5.6% from 5.2% in August – the highest it has been for 20 years.

An increase in energy costs was behind a significant proportion of the increase in the CPI rate, which was up from 4.5% in August.

The CPI index has never been higher, but was also 5.2% in September 2008. The Bank of England’s target rate for CPI is 2%.

This is the first month when benefits will increase in line with CPI instead of RPI.

Rates set by the September inflation figures include allowances and indexation for income tax, national insurance, inheritance tax, capital gains tax, disability and maternity benefits, income support and tax credits.

The increase has put further pressure on the Chancellor, who is battling to reduce the budget deficit, but will provide much-needed relief to claimants struggling to cope with the rising prices of food and fuel.

The Bank of England has already predicted that inflation will hit 5% this year as a result of higher utility bills, but expects price rises to slow in 2012 and 2013.