Prices fell between December and January by more than than a half percentage point.
But a steeper slump in January last year dropped out of the annual reckoning, so year-on-year inflation as measured by Chancellor Gordon Brown's chosen consumer prices index stayed unchanged at 1.6 per cent.
That is comfortably below the Bank of England's two per cent inflation target.
The easier trend after four months of quickening inflation is likely to reassure the Bank of England, which is due to publish its quarterly Inflation Report this morning.
National Statistics said the main factor was a dip the price of petrol and other oil products last month, contrasting with an increase a year earlier.
A seasonal fall in air fares was also greater than last year's, while used car prices rose by less, as did car insurance premiums.
Cuts in prices of both clothing and furniture and furnishing in the January sales were deeper than last year's.
Gas and electricity bills were also up again as utilities phased in their higher tariffs. The cost of fuel and light as recorded by the RPI have now risen by 14 per cent over the past 12 months.
The measure of inflation used until December, 2003 - the RPI not counting mortgage interest - dipped to 2.1 per cent from 2.5 per cent, when it was levelpegging with the Bank's previous target.