UK GAS-Prices edge higher ahead of offshore field maintenance

LONDON, June 7 (Reuters) - British spot gas prices rose on Wednesday as reduced domestic output created a slight supply shortfall and looming offshore maintenance was set to squeeze supply later in the week. * British within-day gas price up by 0.40 pence to 36.30 pence per therm at 0921 GMT. * Day-ahead gas price 0.02 pence higher at 36.00 p/therm. * System undersupplied by 0.8 million cubic metres (mcm), with demand forecast at around 186.4 mcm and flows at 185.6 mcm/day, National Grid (LSE: NG.L - news) data shows. * Forecast demand is 11 percent below the seasonal norm of 207 mcm/day. * Average temperatures for this week were revised upward compared with earlier forecasts, sapping demand. * However, an expected ramp-down in production from the J-Block gas fields from Thursday - ahead of a shutdown planned for Friday - helped to lift spot prices, traders and analysts said. * A dip in supply via the Flags and Vesterled pipelines into the UK also helped to tighten the system. * Total (LSE: 524773.L - news) flows from Norway via the Langeled pipeline rose by 3 mcm to 18 mcm/day. * July gas contract was flat at 36.00 p/therm at 0921 GMT. * Day-ahead gas price at the Dutch TTF hub down by 0.05 euros to 14.80 euros per megawatt hour. * Benchmark Dec-17 EU carbon contract up by 0.03 euro to 5.00 euros per tonne. * Thomson Reuters (Dusseldorf: TOC.DU - news) analyst view: (Reporting by Oleg Vukmanovic; editing by Nina Chestney)