UK GAS-Prompt prices fall on milder temperatures, oversupply

LONDON, March 13 (Reuters) - * British day-ahead gas price down 1.95 pence at 40.15 pence per therm at 0916 GMT. * Within-day contract down 1.70 pence at 39.90 p/therm. * System oversupplied by 37.7 million cubic metres (mcm) per day, with demand forecast at 245.8 mcm/day and flows at 283.5 mcm/day, National Grid (LSE: NG.L - news) data shows. * Traders said forecasts for milder temperatures led to reduced gas demand for heating, while expectations of high wind power output on Tuesday curbed day-ahead gas demand. * Britain's Met Office forecast temperatures could reach as high as 16-17 degrees Celsius in the southeast of the country, quite a few degrees higher than average for this time of year. * Gas demand 8 percent below seasonal norm of 267.6 mcm, National Grid data showed. * Peak wind power output forecast at 4.8 gigawatts (GW) for Monday, rising to 6.8 GW on Tuesday, National Grid data showed. * Imports from Norway through Langeled near full capacity at around 73 mcm/day. * April gas contract down 1.13 pence at 41.30 p/therm. * Winter 2018 contract down 0.50 pence at 47.00 p/therm. * Day-ahead gas price at the Dutch TTF hub down 0.32 euro at 15.68 euros per megawatt-hour. * Benchmark Dec-17 EU carbon contract down 0.07 euro at 5.10 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 Dale Hudson)