* Thursday's gas system seen balanced * Output from Norway's Nyhamna gas field reduced * Set to improve on Friday * Windy Friday pulls down spot power LONDON, Oct 11 (Reuters) - British prompt gas prices eased on Thursday morning as the system was almost balanced and supplies from Norway were expected to improve by the end of the week, analysts said. Gas prices for delivery the next day were trading at 64.45 pence per therm at 0800 GMT on Thursday, down 0.25 pence since Wednesday morning, and prices for delivery within the day were trading at 64.75 pence, down almost one pence per therm. British gas demand was expected to be 199.2 million cubic metres (mcm) on Thursday, around 10 percent below the seasonal norm, according to data from National Grid. With expected flows seen just under 198 mcm, the system would only be slightly undersupplied. The tight system is a result of supply interruptions in Norway. Output from Royal Dutch Shell's Nyhamna gas processing plant in Norway will be reduced by 47 million cubic metres per day on Thursday, gas system operator Gassco said on Thursday. The plant, which processes gas from the giant offshore Ormen Lange gas field before it is shipped to Britain, has an overall capacity of 70 mcm per day, and feeds the Langeled gas pipeline, UK's main undersea gas import route. Analysts said they expected prices to drop further towards the end of the working week as Norwegian exports are set to improve. "Problems at Nyhamna are scheduled to be resolved by tomorrow," analysts at Thomson Reuters Point Carbon said, but added further delays were possible and would pose an upside price risk. Point Carbon also said that because there have not been any imports of liquefied natural gas (LNG) scheduled in recent days, Britain may have to resort to withdrawals from storage. Britain's gas storage sites were filled to an average of 95.79 percent on Wednesday evening, according to data from Gas Infrastructure Europe. Further out on the curve, gas prices for delivery next summer briefly dropped below 61 pence per therm in the morning but rose back to 61.15 pence, following crude oil prices up. Front-month Brent crude prices climbed toward $115 a barrel on Thursday as rising tensions in the Middle East stoked supply fears, keeping prices less than a dollar away from their highest in almost a month, although forecasts of lower demand capped gains. In the power market spot prices also dipped, with contracts for baseload (24s) delivery the next day falling 40 pence per megawatt-hour (MWh) to 45.95 pounds a MWh. Traders said the drop came on the back of typically lower power demand towards the end of the week as well as an expected rise in wind power capacity for Friday. The UK's MetOffice said that it expected Friday's conditions to be "bright and breezy with sunny periods, but quite frequent sharp showers blowing in from the west," with maximum temperatures of 15 degrees Celsius.

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