UK GAS-Prompt prices mixed on revised weather forecasts

LONDON, May 26 (Reuters) - Prompt British gas prices were mixed on Friday morning, as warm weather curbed prices for immediate delivery but forecasts of cooler temperatures next week boosted the day-ahead contract. * British within-day gas price down by 0.65 pence at 36.00 pence/therm at 0841 GMT. * Day-ahead gas price up by 0.40 pence at 36.45 p/therm. * Traders said prompt prices were being driven by the weather, with Britain in the midst of a heat wave, with the highest temperatures forecast on Friday for May since records began. * Britain's Met Office said temperatures could reach up to 30 Celsius in parts of the country on Friday, but are likely to fall after the weekend, with highs around 21 degrees C predicted for Monday. * Gas system oversupplied by 10.7 million cubic meters (mcm), with demand forecast at 168.3 mcm and flows at 179 mcm/day, National Grid (LSE: NG.L - news) data showed. * Gas demand 18 percent below seasonal norm of 206 mcm, National Grid data showed. * June gas contract up by 0.47 pence to 36.55 p/therm * Summer 2018 contract up by 0.07 pence to 39.95 p/therm * Day-ahead gas price at the Dutch TTF hub up by 0.13 euro to 15.13 euros per megawatt hour. * Benchmark Dec-17 EU carbon contract up by 0.11 euro to 5.09 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 Nina Chestney)