Headline inflation decelerated in April, with consumer prices increasing at an annual pace of 4.2 per cent, down from 4.6 per cent in March.Automotive fuel prices fell 7 per cent in April after rising 32.8 per cent in the previous month. The fall in fuel prices included the halving of the fuel excise on April 1, a measure introduced by the federal government to shield motorists from the global energy shock.Trimmed mean annual inflation, which is the Reserve Bank's preferred measure of underlying inflation, was 3.4 per cent in the 12 months to April, slightly up from 3.3 per cent in March.