* UK Aug PPI output price inflation +4.7 percent vs +5.0 pct
* Input prices unexpectedly fall 0.5 percent on month
* Oil pushes costs down but higher wheat prices a worry
(Adds economists' reaction)
By David Milliken and Christina Fincher
LONDON, Sept 10 (Reuters) - British annual factory gate inflation slowed more than expected to a six-month low in August, helped by a surprise fall in input prices on the month driven by oil, official data showed on Friday.
The Office for National Statistics said producer output price inflation fell to 4.7 percent last month from 5.0 percent in July, just below the consensus forecast for an annual rise of 4.8 percent and the fourth consecutive decline.
The figures will be welcomed by the Bank of England which has partly blamed the cost of imported commodities for the stickiness of above-target inflation.
"It's a better-than-expected report which suggests that some progress is being made in alleviating factory gate inflation, albeit largely due to the effect of energy costs," said Philip Shaw, UK economist at Investec.
Gilt prices and sterling were little changed.
"The Bank of England will probably be pretty happy with the August producer price data and the figures reinforce the belief that the Monetary Policy Committee will hold off from raising interest rates for some considerable time," said Howard Archer, economist at IHS Global Insight.
Producer output prices were unchanged on the month, with a fall in the cost of petroleum products being offset by a rise in the cost of food and other products.
Input price inflation slowed even more sharply, dropping to an annual rate of 8.1 percent from 10.8 percent in July -- well below forecasts of 8.9 percent and the weakest rate since February.
On the month input prices dropped 0.5 percent, wrong-footing analysts who had expected a slight rise.
The main downward contributor was crude oil which fell 1.3 percent on the month, knocking 0.3 percentage points off the broader index.
On the year crude oil input price inflation more than halved to 11.8 percent from 24.4 percent in July, its lowest rate since October 2009.
But the cost of home-produced food materials rose 1.4 percent on the month, making them the fastest rising component of input prices. The ONS said this was largely due to a rise in wheat prices in global markets.
Russian wheat output has been decimated by the country's worst drought in 130 years, and global wheat prices are now 60 percent higher than in late June.
"Rising food crop prices are a considerable concern," Global Insight's Archer said.
(Editing by Toby Chopra)