UK GAS-Prices edge up on lower Norwegian imports

* Langeled flows down to around 20 mcm/d

* Power prices down on improved nuclear output

LONDON, April 22 (Reuters) - British spot gas prices rose slightly on Tuesday as a cut in imports from Norway left the system undersupplied.

Gas prices for delivery the next day were trading at 50.40 pence per therm at 0515 GMT on Tuesday, up 0.55 pence since opening, and prices for within-day delivery were up 0.05 pence at 50.65 pence a therm.

Traders said that these slight price rises were a result of an undersupplied system following a cut in Norwegian supplies.

"Flows through the Langeled pipeline from Norway are down this morning due to gas field maintenance at the Heimdal Riser platform in the North Sea," one trader said.

Flows through the 70 million cubic metres (mcm) per day capacity Langeled pipeline were down from 30 mcm overnight to just over 20 mcm on Tuesday.

In Britain's wholesale power market, prices for baseload (24 hours) delivery on Wednesday were down almost one pound ($1.68)per megawatt-hour (MWh) to 42.05 pounds per MWh on the back of improved nuclear power plant availability.

Two nuclear reactors with a combined capacity of 1,040 MW are currently off the grid, down from four reactors with a total 2,230 MW earlier in April.

GAS UK natural gas prices National Grid (LSE: NG.L - news) instant flows National Grid gas demand North Sea gas and power maintenance

POWER UK: baseload prices , peakload prices , outages FRANCE: baseload prices , peakload prices , outages, report GERMANY: baseload prices , peakload prices , outages, report CENTRAL EUROPE: report SWITZERLAND: outages, reservoir levels NORDIC (SES: MR7.SI - news) : report EU CARBON PRICES SPEEDGUIDE:

($1 = 0.5951 British pounds) (Reporting by Alexander Winning; Editing by Susan Fenton)