(Updates with oil price turning down)
By Jeremy Gaunt, European Investment Correspondent
LONDON, Sept 1 (Reuters) - Financial markets began the month in a volatile mood on Monday with economic fear driving equities lower and gloom about Britain's downturn knocking sterling to a 12-year low.
The price of oil swung from being up well over $1.50 a barrel to registering losses of around $1.75 as Hurricane Gustav showed no signs of strengthening in its way towards the U.S. state of Lousiana.
Investors also were unhappy with Commerzbank's <CBKG.DE> $14.5 billion purchase of Dresdner Bank from Allianz <ALVG.DE>.
The dollar was generally stronger and short-term euro zone government bond yields fell as investors bought into safe-haven plays. U.S. markets were closed for the Labor Day holiday.
Investors are mostly concerned at the moment with worries about the depth of a global economic slowdown.
This was clearest on Monday on currency markets, where Britain's pound fell to a 12-year low on a trade-weighted basis.
It was also down three-quarters of a percent at around $1.80 <GBP=> against the dollar, its lowest since April 2006 and a sharp comparison with more that $2 in July this year.
The declines followed Chancellor of the Exchequer (finance minister) Alistair Darling's comments that the UK's economic downturn is likely to be deeper and last longer than originally feared and might turn out to be the worst for 60 years.
"Most people believed that things were probably deteriorating faster in the UK than the government was admitting, but the fact that we've seen the chancellor come out and admitting that things are far worse have put sterling under pressure," said Ian Stannard, senior currency strategist at BNP Paribas.
GUSTAV BLOWS
Crude oil prices <CLc1> initially rose above $118 a barrel Gustav shut down nearly all offshore oil output in the U.S. Gulf and threatened the Louisiana coast.
Prices reversed, however, as forecasts showed the storm was not strengthening beyond earlier projections. U.S. light crude for October delivery was down $1.71 at $113.75 a barrel.
"Gustav is not strengthening," said Mike Wittner of Societe Generale. "That could be bearish."
The storm, however, is the biggest threat to the region -- home to a quarter of U.S. oil output and 15 percent of natural gas output -- since Hurricanes Katrina and Rita wrecked more than 100 offshore oil platforms in 2005 and closed several large refineries for months.
Nearly 2 million people have fled the U.S. coastal areas.
TOO MUCH
Equity markets, in the meantime, were kicking off the month on a down note, generally gloomy about the economic outlook.
European shares fell sharply in early trade, led by banks as Commerzbank tumbled more than 6 percent after agreeing its deal to buy Dresdner.
The FTSEurofirst 300 index of top European shares <
> was down around 0.9 percent, starting the month off on a weak note after notching up a gain of 1.2 percent in August, only its second monthly gain in 10 months. Allianz was flat.Investors appeared to believe the deal was too expensive. "On a first glance we don't like the transaction at all," DZ Bank said in a note.
Earlier, Japan's Nikkei stock average <
> shed 1.8 percent as Honda Motor Co <7267.T> and other exporters fell on worries about the economy and a slightly stronger yen.The benchmark Nikkei shed 238.69 points, completely erasing last week's gains, to finish at 12,834.18. The broader Topix <
> lost 1.9 percent to 1,230.64.Euro zone government bond prices shot higher after the gloomy comments from Britain's Darling triggered concern that a similar outlook would be felt throughout the euro zone.
Two-year yields fell 6 basis points to 4.061 percent <EU2YT=RR> while 10-year yields were 1 basis points down at 4.161 percent <EU10YT=RR>.