UK gas prices rise on tight supplies

* UK system seen 3.8 mcm/d undersupplied

* Market prices in Norway supply risk

LONDON Oct 18 (Reuters) - British gas prices rose on Thursday morning as the system was slightly undersupplied and cool weather kept demand relatively high.

Gas for day-ahead delivery traded up 0.65 pence per therm between Wednesday and Thursday morning to 64.10 at 0745 GMT, and prices for delivery within the day were trading at 64 pence.

Gas demand was expected to be 205.8 million cubic metres (mcm) on Thursday, according to data from National Grid, but with flows only seen at 202 mcm, the system was seen slightly undersupplied.

The reduction in supplies was largely a result of a slight reduction in Norwegian exports to Britain, which slipped by 5.3 mcm to 96.4 mcm on lower flows through the Vesterled pipeline.

"There's a clear risk premium in the market at the moment as the market remains tight although it's not even very cold yet," one gas trader said.

"We're worried what will happen once it really gets cold across Europe, especially should there be glitches in Norwegian supplies again and the dearth of LNG imports to Britain continue," he added.

The bullish trend was also filtering further out into the curve, with November gas prices trading around 94.90 pence a therm, close to their October high of 94.95 pence.

"64.95 is the October high, above which 68.00 and 70.75 are the next clear targets on the continuation chart," energy brokers GFI said in their Thursday morning market note.

On the far end of the curve, gas prices for delivery in summer 2013 were also bullish, testing resistance at 62 ppence per therm, although technical indicators were sending mixed signals.

The contract's relative strength index (RSI), at over 64, points, is getting close to 70 points, which would imply an overbought market.

On the bullish side, the 50 exponential daily moving average (DMA) value has crossed its 200 DMA equivalent and is now above both its 100 and 200 DMAs for the first time since Q3 last year. (Reporting by Henning Gloystein, editing by William Hardy)