* March CPI rises to 3.4 percent y/y vs 3.2 percent forecast
* Transport costs, gas bill base effects drive increase
* Gilt futures fall on worries about inflation outlook
(Adds detail, reaction)
By David Milliken and Christina Fincher
LONDON, April 20 (Reuters) - British annual consumer price inflation rose more than expected in March, pushed up by higher transport costs, and gas bills which failed to repeat last year's fall.
The Office for National Statistics said consumer price inflation increased to 3.4 percent last month from 3.0 percent in February, well above the Bank of England's 2 percent target and economists' expectations of a rise to 3.2 percent.
Gilt futures fell around 20 ticks on the news to a session low, as the data casts some doubt on whether inflation will ease as rapidly this year as the Bank of England assumed in its February inflation forecasts.
"Unless we get a sharper collapse in oil prices, inflation may remain a little bit higher than we thought a few months ago," said Peter Dixon, economist at Commerzbank.
However, other analysts were more sanguine, noting that for the first quarter as a whole inflation has been broadly in line with the Bank of England's central projection of just over 3.3 percent.
The BoE still has interest rates at a record low 0.5 percent, and completed 200 billion pounds of quantitative easing in February, and few economists have forecast a tightening in policy before late this year.
Economists still expect a gradual fall in inflation, as the one-off effects pushing up March's annual CPI rate are slowly outweighed by weak growth and high unemployment, which limit the ability of firms and workers to raise prices and wages.
The failure of household gas bills to repeat last year's record fall accounted for a quarter of the increase in the annual rate between February and March.
Higher air fares and petrol prices together contributed a similar upward thrust, and a rise in food and drink prices was the third-biggest factor.
On the month, consumer price inflation was 0.6 percent, twice as high as analysts expected and above the 0.4 percent rate recorded in February.
The retail price inflation gauge -- which includes a broader range of housing costs -- hit its highest since September 2008, rising to 4.4 percent from 3.7 percent, versus forecasts for a rise to 4.2 percent. RPI is used to index many social security payments and some wages.
Within the CPI basket, the biggest rise came from transport, which was up a record 11.3 percent on the year. Communication costs rose by 4.9 percent, again the highest annual rate since records began in January 1997.
Clothing and footwear prices fell at the slowest annual pace since July 2007, down 2.6 percent on the year, and services overall rose at their fastest rate since last May.
British inflation has proven surprisingly sticky given that the economy has been through its sharpest contraction since World War Two, and economists say sterling's weakness may be partly to blame.
"The main difference relative to our forecasts is from clothing and footwear which raises the risk that it is something to do with sterling," said George Buckley, economist at Deutsche Bank.
Sterling dropped by around a quarter on a trade-weighted basis between mid-2007 and mid-2009, and much of a partial recovery in late 2009 has been eroded since the start of this year. (Editing by Stephen Nisbet)