* Bacton Shell resumes output * Shell's St Fergus terminal nears end of maintenance * Norway's Sleipner gas field startup delayed * More LNG to arrive in Europe this winter: DONG Energy LONDON, Sept 7 (Reuters) - British prompt gas prices fell on Friday morning as supplies from the UK Continental Shelf rebounded and exports towards Belgium were reduced. Gas for weekend delivery fell 0.40 pence to 60.10 pence a therm, while month-ahead gas shed nearly half a penny to 59.75 pence. Prices softened despite evidence of mild gas shortages at the British hub, undersupplied by 3 million cubic metres/day (mcm/day), according to National Grid data. The availability of flexible supplies to the UK grid such as stocks held in storage, combined with a cummulative growth in domestic supply as a result of reduced exports during the course of the day, may provide enough swing to plug supply gaps. Gas prices on Thursday had risen to a four-month high as maintenance in the North Sea and a lack of liquefied natural gas (LNG) supplies led to tightness in the system, but prices backtracked once Shell reopened its Bacton terminal. "Supply is still pretty dreadful but demand is also pretty dreadful," a trader from a UK utility said on Friday, explaining that the two are largely offseting one another. "Yesterday was the worst day in terms of supply that I have ever seen," the trader added. Flows from Shell's Bacton terminal, which dropped to zero in the previous session, recovered to 12 mcm/day earlier this morning. A five-day maintenance outage is scheduled to start at the terminal from Sept. 10, Shell said. Shell's St Fergus terminal is under maintenance until Sept. 10, while work on an entry point for Norwegian into the British transmission system will interrupt flows from the same date. Other maintenance is also interrupting pockets of North Sea activity in British and Norwegian waters, leading to further supply tightness. UK gas output rose to 57 mcm/day, up 4 mcm/day on the previous day. Expected exports to Belgium fell by half to 4 mcm/day. Startup of Norway's Sleipner gas field in the North Sea has been delayed for two days until Sunday morning, gas system operator Gassco said on Friday. The Statoil operated facility was expected to restart production on Friday at 0400 GMT after a planned maintenance, which started on August 18. LNG terminal output fell as the system appeared more balanced, with fairly minor flows issuing from the Isle of Grain and South Hook terminals. European LNG imports are set to rebound this winter and drive down rising prices as slumping demand in Asia fails to stage a recovery this year, the head of LNG at DONG Energy said in an interview. "The result of the leveling out of demand in Asia increases the LNG availability for Europe, putting pressure on European gas prices, especially in the UK," Steen Kallestrup, head of the Danish firm's LNG business, told Reuters on Thursday. Higher gas supplies resulting from diversions may eventually translate into lower energy bills for cash-strapped British consumers. Winter 2012 gas prices softened to 66.45 pence, down 0.45 pence on the day as bearish prompt fundamentals fed into longer-dated contracts. In Britain's power market the day-ahead contract fell to 42 pounds per megawatt hour, down about 1 pound on Thursday's session on the back of weaker gas prices.

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