* Norwegian supply cut equates to 19 pct of UK demand
* Above-average temperatures weigh on demand (Recasts lead)
May 23 (Reuters) - British spot gas prices rose on Wednesday after a cut in Norwegian supply due to a false alarm at the Troll platform left the pipeline network short.
Norwegian gas flows via the Langeled pipeline - Britain's main sub-sea import route - more than halved to 20 million cubic meters/day (mcm/day) after Statoil suspended production at Norway's biggest gas field at 1859 GMT on Tuesday.
At forecast demand of 200 mcm, the cut in flows is equivalent to about 19 percent of Britain's total gas consumption.
"There was a false gas alarm on (gas platform) Troll A yesterday evening," field operator Statoil spokesman Ola Anders Skauby said in a text message to Reuters.
"According to procedures, production was shut down and personnel without emergency response tasks were mustered in the lifeboats. The situation was normalised after 15 minutes," he added.
Skauby had no information on when full production could be expected again.
Supply restrictions spurred Wednesday gas 1.50 pence higher to 53.50 pence per therm at 1001 GMT. By contrast, Thursday gas was little changed at 53.30 pence, down just 0.10 pence.
Lower forecast demand and the expected restart of flows via the Theddlethorpe terminal in southeast England pushed down gas prices for next-day delivery, analysts from Point Carbon said.
The pipeline network was 13 mcm/day undersupplied earlier in the day, narrowing to a shortfall of just 3 mcm/day by 1037 GMT, flow data showed.
Above-average temperatures forecast this week across England, Wales and Scotland weighed on prices as households turned down heating.
Temperatures are expected to reach sustained highs in the mid-20 degrees Celsius range in parts of the country during the week, forecasters said.
"A high will dominate the weather this 10-day period giving dry and warm summer conditions. From some days into next week a slow change to cooler conditions," forecasters from Point Carbon said.
Forecaster Weather Services International (WSI) also said on Monday that average summer temperatures across Europe will be higher than normal between June and August, with the exception of southeastern parts of the continent.
Further forward, the benchmark winter 2012 gas contract slumped nearly a penny to 65.75 pence as growing hopes of a deal between Iran and the U.N. nuclear watchdog eased potential supply concerns and pulled Brent crude oil prices lower.
In the power markets, baseload day-ahead power for 24-hour delivery fell 25 pence to 40.90 pounds per megawatt hour. (Reporting by Oleg Vukmanovic, editing by William Hardy)
