* UK gas system seen 23.6 mcm/d undersupplied
* Output from Nyhamna gas plant reduced by 35 mcm/day
* Colder weather lifts demand
LONDON, Oct 10 (Reuters) - British prompt gas prices rose onWednesday as higher demand and shortages caused by lowerNorwegian exports left the market short by 23.6 million cubicmetres (mcm), National Grid data showed.
Gas for day-ahead delivery rose by 0.70 pence per therm onWednesday morning to 64.70 pence at 0820 GMT.
"Norwegian supply is getting shakier just as gas demand inthe UK is picking up, so the market is putting a risk premium onprices here," one gas trader said.
Flows through the Langeled pipeline that connects Norwaywith Britain dropped to around 13 mcm this morning, NationalGrid data showed.
Norwegian gas exports have been hit by disruptions at RoyalDutch Shell's Nyhamna gas processing plant, where output hasbeen cut by 35 mcm per day for an unknown duration due to a pumpfailure, gas system operator Gassco said on Wednesday.
Britain's gas market supply was expected to be 182.9 mcm onWednesday, National Grid data showed, leaving the market shortwith demand running just 6 percent below seasonal average at206.5 mcm.
Traders said colder weather has helped to lift demand whichwas languishing around 30 percent lower than the season averagefor much of last week, before the temperature dropped.
Further out on the curve the Summer 2013 contract ticked up0.08 pence to 61.13 pence per therm with gains contained by asluggish oil market.
Front-month Brent crude prices slipped to near $114 perbarrel on Wednesday morning as fears about demand, due to theweak global economic outlook, halted bullish sentiment that hadseen the contract rise 2 percent the previous session.
Analysts at Societe Generale said the Summer 2013 gas pricelooks vulnerable at these high levels.
"At today's prices gas is too expensive a fuel for Europe.We therefore remain more bearish than the future curve. Werecommend selling NBP Summer 13 as we believe the forward curvehas not taken into account the 11bcm of gas already 'pre-paid'by European companies," Societe Generale said in a research noteon Wednesday.
In Britain's power market prompt prices edged higher on theback of the tightness in the gas system and the colder UKweather.
Prices for baseload day-ahead power rose 53 pence to 46.28pounds per megawatt hour (MWh).
(Reporting by Susanna Twidale, additional reporting by HenningGloystein; editing by James Jukwey)
((susanna.twidale@thomsonreuters.com +44)(0)(207 5424753))
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Keywords: MARKETS BRITAIN GAS/POWER