UK GAS-Prompt prices edge higher on slight undersupply

LONDON, April 19 (Reuters) - Prompt British wholesale gas prices edged higher on Wednesday in a slightly undersupplied system. * British day-ahead gas price up by 0.40 pence to 39.80 pence per therm at 0926 GMT. * Within-day contract up by 0.50 pence to 39.70 p/therm. * System undersupplied by 4.9 million cubic metres (mcm) with demand forecast at 264.9 mcm, and flows at 260 mcm/day, National Grid data shows. * "The prompt is a touch firmer on the undersupply, but further out prices are weaker," a gas trader said, adding the further out prices were dampened by expectations of warmer weather. * Imports from Norway through the Langeled pipeline were around 48 mcm/day, down from around 55 mcm the previous day. * May gas contract down by 0.10 pence to 39.35 p/therm. * Winter 2017 contract down by 0.23 pence to 47.15 p/therm. * Day-ahead gas price at the Dutch TTF hub up by 0.05 euro to 16.45 euros per megawatt hour (MWh). * Dutch gas prices for Winter 2017 up by 0.10 euro to 17.70 euros/MWh. * Traders said Dutch curve prices were boosted by news late on Tuesday that the Netherlands will reduce production at its Groningen gas field by 10 percent from October to limit the risk of earthquakes. * Output has been cut several times from 53.9 billion cubic metres (bcm) in 2013 to 24 bcm, as criticism mounted that Dutch authorities had failed to adequately assess the risk to citizens from earthquakes caused by production at Europe's biggest field. * Benchmark Dec-17 EU carbon contract up by 0.01 euro to 4.87 euros per tonne. * Thomson Reuters (Dusseldorf: TOC.DU - news) analyst view: http://emea1.apps.cp.extranet.thomsonreuters.biz/cms/?pageid=united-kingdom-gas (Reporting By Susanna Twidale; Editing by Susan Fenton)