* Yemen LNG denies new attack on supply line * Winter 2012 gas tracks rising oil price LONDON, Sept 4 (Reuters) - British month-ahead gas prices rose on Tuesday on supply concerns after Qatargas, the world's largest exporter of liquefied natural gas (LNG), said it planned to shut two production lines for maintenance this month. October gas rose 0.25 pence to 60.45 pence ($0.96). "The question is whether it will impact the rest of the curve," a source at a UK utility said, referring to later-dated gas contracts. Britain depends on Qatar for a rising share of its seaborne gas needs. Any impact on LNG deliveries will become evident only in October, because it takes around two weeks for shipments from the Middle East to reach the UK. Qatargas will shut production trains 4 and 5 this month, but last week also said it had shut train 7 because it needed a new motor. Yemen LNG, meanwhile, dismissed reports of an explosion on the pipeline that feeds gas to its export terminal. The last attack on the pipeline was on Aug. 21, and it was repaired and reopened at the end of last month. Gas for delivery on Wednesday and for the rest of the week was unchanged at 60 pence a therm. Further forward, the benchmark winter 2012 gas contract took direction from rising crude oil prices, up 0.15 pence to 67.25 pence. Gas prices for next summer rose in tandem at 61.9 pence, up 0.15 pence. Oil rose for a fourth day amid hopes of further stimulus from central banks in the United States and Europe. Britain's gas market was undersupplied by 9 million cubic metres/day (mcm/day), with demand pegged at 141 mcm/day. Subdued trading activity on the UK gas market comes after a sharp rally during Monday's session, driven by gas shortages primarily caused by a reduction in flows from the South Hook LNG terminal. A trader on Tuesday said the reduction was not caused by maintenance or capacity restrictions imposed at the terminal. South Hook, which relies on Qatari LNG imports, raised send-outs from 14 mcm/day on Monday to about 17 mcm/day early on Tuesday. South Hook is due to receive an LNG delivery on Tuesday, which could explain the rise in flows. Britain reduced exports to Belgium and storage injection rates to help plug the gap between supply and demand, providing added flexibility to the system, analysts at Point Carbon said. "Norway's Langeled pipeline is currently flowing at 37 mcm/d to Britain, up from yesterday's level ... This is likely a result of rerouting gas from Zeepipe, which is on maintenance," Point Carbon said.($1 = 0.6292 British pounds) (Reporting by Oleg Vukmanovic; editing by Jane Baird)

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