LONDON, March 23 (Reuters) - British spot gas prices hit an 8-week low on Friday thanks to rising temperatures, oversupply and swelling inventories, while summer gas extended its premium over near-term prices. Gas for immediate delivery fell 1.45 pence to 55.60 pence per therm, showing an unusual discount of 3.4 pence to the benchmark summer 2012 contract. Expectations of higher prices this summer encouraged further injections into underground storage sites, with the UK's biggest facility Rough now twice as full as last year at 49 percent. Stock levels at the UK's South Hook liquefied natural gas (LNG) terminal have risen to near maximum levels as low demand and slumping prices kept a lid on send-out. LNG terminal output in March fell 52 percent over the prior year, although South Hook flows will likely increase to clear storage space ahead of a cargo delivery due next Friday. Summer gas prices typically trade at discount to other contracts. This year, however, geopolitical tensions with Iran and the threat of Middle East supply disruptions have spurred crude oil prices higher, also lifting summer and winter gas prices. In contrast, near-term gas prices have been pressured lower by an unusually mild winter and low demand, leading to spot prices trading at a discount to forward contracts. That reversal has prompted an early start to the storage injection season, as players store cheap gas now to sell at a higher price in the summer. Forecasters see above-temperatures turning cooler from next weekend. South-western parts of the UK will see temperatures reaching highs of 19 degrees Celsius this weekend. Despite weak demand, increasing exports to mainland Europe and rising demand for storage injection may limit the downward pressure on prices, analysts from Point Carbon said. A planned halving in storage injection capacity at Rough between March 26-31 provides a bearish price signal, since it may reduce injection demand and lead to oversupply. (Reporting by Oleg Vukmanovic, editing by William Hardy)

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