UK GAS-Within-day gas declines on oversupply

LONDON, March 20 (Reuters) - British wholesale gas for immediate delivery declined on Monday morning due to oversupply, traders said. * The within-day contract was 0.55 pence lower at 40.35 pence per therm at 0935 GMT. * Demand was forecast at around 236 million cubic metres (mcm) and flows at 255 mcm/day, leaving the system oversupplied by 19 mcm, National Grid (LSE: NG.L - news) data shows. * Flows from Norway through the Vesterled pipeline are higher at 15 mcm. * Exports through the InterconnectorUK pipeline to continental Europe are nominated at 10 mcm, 5 mcm lower than on Friday. * The day-ahead gas price was 0.62 pence higher at 41.20 pence per therm. * Day-ahead consumption is forecast 37 mcm higher at 188 mcm, according to Thomson Reuters (Dusseldorf: TOC.DU - news) analysts. Gas-for-power demand for Tuesday is forecast 7 mcm higher at 53 mcm. * Peak wind generation is expected to be 7,855 megawatts (MW) on Tuesday from 7,915 MW on Monday, Elexon data shows. * Total (LSE: 524773.L - news) 's Bacton Seal will undergo an outage from March 26-27 which will reduce capacity by 12.6 mcm/day due to a production cut at the Elgin Franklin field. * Further along the curve, the April gas contract was down 0.74 pence at 40.95 pence per therm. * The Dutch day-ahead gas price at the TTF hub inched up by 0.03 euro to 15.73 euros per megawatt hour. * The benchmark Dec (Shanghai: 600875.SS - news) -17 EU carbon contract inched down by 0.04 euro to 5.10 euros a tonne. (Reporting by Nina Chestney)