Britain's Consumer Prices Index (CPI) in May dropped further to 2.8 percent from April's 3 percent, reaching a two-and-half year low, the Office for National Statistics said on Tuesday.

The fall, mainly due to a weakening impact of the VAT rise in 2011 as well as falling or slowing commodity and food prices, was out of market expectation which had forecast an unchanged inflation rate in May.

The Retail Prices Index (RPI) measure also fell from 3.5 percent in April to 3.1 percent in May.

Average diesel prices fell by 4.4 pence to 143.3 pence per liter between April and May, while food and drink prices rose by just 0.3 percent compared with a 1.3-percent rise last year.

Analysts expect the easing inflation would further increase the possibility of further quantitative easing (QE) by Bank of England, as Governor Mervyn King warned last week that the case for a QE is "rising."

The Bank of England has predicted that CPI inflation rate will likely remain above its target of 2 percent for "the next year or so."