* Demand remains low at 26 pct below seasonal norms
* Power flat as nuclear restart counter-balanced by gas rise
LONDON, July 25 (Reuters) - British prompt gas prices traded higher on Wednesday as imports from Norway via the Langeled pipeline halved, leaving the UK gas market short of supply.
Gas for day-ahead delivery rose 0.70 pence to 54.00 pence per therm, while within-day gas added 1.35 pence to 54.45 pence.
"The system opened really short with Langeled flows down to just 30 mcm (million cubic metres)," one UK gas trader at a utility said.
Flows through the pipeline dropped from around 63 mcm/d at the start of the gas day at 0600 BST, leaving the UK market undersupplied by around 24 mcm/d, National Grid data showed.
Demand fundamentals remained weak with consumption tagged 26 percent below seasonal norms at 176 mcm/d.
The outlook for additional liquefied natural gas (LNG) supply improved, however, as two tankers are expected to berth in Britain on Friday and one more ship is due to arrive next week, providing some supply outlook relief.
Further out, the benchmark front-season contract also traded slightly higher, adding 0.05 pence day on day to 61.90 pence, reflecting gains on the prompt.
The crude market provided little direction as it traded near $103 per barrel.
In Britain's electricity market, spot prices were flat day on day as additional supply from the restart of a nuclear power reactor was counter-balanced by gains in the gas market.
Day-ahead baseload power traded at 42.55 pence.
EDF Energy restarted its 660-MW Heysham 2-7 nuclear unit early on Wednesday following an outage on Sunday.
The market also awaited a decision by the European Commission to set aside carbon permit supply to stem a continuous fall in CO2 prices. (Reporting by Karolin Schaps; Editing by Alison Birrane)