The fall in inflation points to some easing of the huge pressure on household budgets, as well as giving the Bank's Monetary Policy Committee greater scope to support the economy as the Coalition Government's spending cuts weigh on consumer confidence and the eurozone crisis looms large.
A 4.5p fall last month in the price of a litre of petrol, to £1.37, and a much smaller rise in the price of food and non-alcoholic beverages this May than last played significant parts in pushing down the annual consumer prices index inflation rate.
And clothing and footwear prices fell by 0.1% last month, having risen by 0.4% in May 2011.
The fall in inflation took the City by surprise when it was announced by the Office for National Statistics yesterday. The consensus forecast among economists had been that annual consumer prices index (CPI) inflation would have remained at 3% last month.
May's 2.8% figure is the lowest since a rate of 1.9% in November 2009, although still above the 2% target set for the MPC by the Treasury.
The MPC last month projected that annual UK CPI inflation would undershoot the 2% target on a two-year time horizon even if base rates were to remain at a record low of 0.5% and the scale of a quantitative easing programme aimed at stimulating activity were to be held at £325 billion.
The UK fell back into recession with a second consecutive quarterly fall in gross domestic product in the opening three months of this year.
UK GDP fell by 0.3% in both the final three months of 2011 and the first quarter of this year, and economists fear another decline in the three months to June given a slew of weak economic indicators and the extra bank holiday for the Queen's Diamond Jubilee.
The UK's domestic economic troubles have been exacerbated in recent months by an escalation of the eurozone crisis.
Spain's latest bond auction yesterday underlined the high interest rates which it is having to pay to raise debt, and the situation in Greece remains grim.
Esmond Birnie, chief economist in Scotland and Northern Ireland for accountancy firm PricewaterhouseCoopers, said: "Declining oil prices are beginning to feed through into petrol and diesel prices at the pumps, retailers are engaged in some aggressive price cutting and even the cost of some fruit and vegetables have fallen sharply, thanks to a bumper harvest."
He added: "Whilst inflation remains above the Bank of England's 2% target, (the) data could be significant on a couple of fronts. First, the Monetary Policy Committee may judge that it gives them more room for manoeuvre for possibly introducing further quantitative easing. And, second, anything which reduces the previously severe squeeze on household disposable incomes might stir a revival in consumer spending and hence turn the economy to a more general and durable recovery."
Quantitative easing, implemented through the purchase of Government and corporate bonds using central bank reserves, is aimed at increasing money supply and stimulating activity.
Bank of England Governor Sir Mervyn King, in his speech to the City at the Mansion House in London last week, highlighted the potential to increase QE further if needed.
Minutes of the nine-strong MPC's June 6 and June 7 meeting will today provide further clues on how close committee members might be to sanctioning further quantitative easing.
Vicky Redwood, chief UK economist at consultancy Capital Economics, said: "The MPC would not have seen these figures at its meeting earlier this month. Mervyn King has already hinted strongly that more quantitative easing will soon be forthcoming and these figures might help to tip any of the more reluctant members into voting for more stimulus at the upcoming meeting."