UK GAS-Mild weather dampens demand, prices slip

March 8 (Reuters) - * British day-ahead gas price down 0.55 pence to 42.15 pence per therm at 0903 GMT. * Within-day contract down 0.55 pence to 42.25 p/therm. * System oversupplied by 5.8 million cubic metres (mcm/day) with demand forecast at 262.2 mcm, and flows at 268 mcm, National Grid data shows. * Traders say milder weather has cut demand for gas-fired heating with above-average temperatures forecast for next week. * Heating demand forecasts for day-ahead fall to 166 mcm/day -- 41 mcm/day below the seasonal average, Thomson Reuters (Dusseldorf: TOC.DU - news) analysts said. * Production at Britain's North Morecambe gas terminal at zero until April 1 due to a planned outage, while an outage also cut output at the Laggan Tormore gas field * April gas contract down 0.70 pence to 42.20 p/therm. * Winter 2017 contract down 0.50 pence to 47.60 p/therm * Day-ahead gas price at the Dutch TTF hub down 0.13 euros to 16.27 euros per megawatt hour. * Benchmark Dec-17 EU carbon contract down 0.09 euro to 5.29 euros per tonne. * Thomson Reuters analyst view: (Reporting by Oleg Vukmanovic in Milan; Editing by Alexander Smith)