June 21 (Reuters) - British wholesale prompt gas prices rose on Wednesday morning as lower imports and domestic production curbed supply.
* The British within-day gas price was up by 0.4 pence at 35.2 pence/therm at 0900 GMT.
* The day-ahead gas price rose by 1 pence to 35 pence/therm.
* Traders said that reduced imports from Norway, combined with lower domestic production in Britain because of maintenance, had left the market undersupplied, boosting prices.
* Two unplanned outages at the Nyhamma gas plant and Visund gas field cut Norwegian production, operator Gassco said.
* Imports to Britain from Norway through the Langeled pipeline were around 18 mcm, down from more than 30 mcm the previous day.
* Maintenance at Britain's Laggan Tormore gas field, from June 17-24, cut UK domestic gas output.
* Demand for gas to be used in power plants was firm on forecasts for low wind power output.
* Peak wind power generation is forecast at 4 gigawatts (GW) on Wednesday and 3.6 GW on Thursday, National Grid data showed.
* Wind power met about 7.6 percent of Britain’s electricity demand on Wednesday morning, while gas-fired plants provided more than 50 percent, the data showed.
* The British wholesale day-ahead electricity price was up by 2.65 pounds at 41.25 pounds per megawatt hour (MWh)
* The July gas contract rose by 0.17 pence to 36 p/therm.
* Day-ahead gas at the Dutch TTF hub was up by 0.06 euros at 15.32 euros/MWh.
* Thomson Reuters (Dusseldorf: TOC.DU - news) analyst view: http://emea1.apps.cp.extranet.thomsonreuters.biz/cms/?pageid=united-kingdom-gas (Reporting By Susanna Twidale; Editing by David Goodman)