British gas prices firmed early on Thursday following a strong rally in the U.S. natural gas market overnight and firm oil prices, while prompt power prices eased on solid supply margins.

Gas for Friday put on 0.60 pence to 21 pence per therm ($3.48 mmbtu) by 0900 GMT, while October was up 0.5 pence to 24.4 pence and November rose 0.8 pence to 33.95 pence.

The most important thing is the US gas market, said a trader. It's the momentum. We've got a bull run at the moment...but they'll come down again. More fields are coming back next week. Also LNG will come.

Port authority data showed the Excellence liquefied natural gas (LNG) tanker was to berth at Dragon terminal on Sept. 23.

A volatile supply from Norway via the Langeled pipeline also helped push up prompt contracts. While there was a surplus in the system early on Thursday, physical flow was forecast to stand below predicted demand.

Overnight, New York Mercantile Exchange natural gas futures ended sharply higher, again driven by a flood of technical buying and short-covering despite concerns about record high inventories, mild U.S. weather forecasts and a sluggish economy.

Oil stood at around $72 a barrel after a rise of more than 2 percent on Wednesday, following a larger-than-expected fall in U.S. crude oil inventories. [O/R]

Total's Elgin-Franklin gas field restarted early Wednesday, after an unplanned outage on Tuesday, but gas flow through Bacton SEAL stayed at 10 mcm, the National Grid website showed.

Shell, which operates gas fields that feed into Bacton SEAL, would not comment on maintenance schedules.

Theddlethorpe terminal was still offline.

Along the curves, gas for the 2010 first quarter was up 0.6 pence to 38.8 pence, while the 2009 winter climbed 0.9 pence to 35.35 pence.

In the power market, prompt prices were soft, with fewer plant outages creating a solid supply margin.

Baseload power for Friday -- when typically demand is smaller ahead of the weekend --- stood at 32 pounds per megawatt hour, with exports to continental Europe resuming early in the morning. Day ahead contracts were 32 pounds late on Wednesday.

October eased to 34.70 pounds from 34.80 pounds, while November fetched 38.75 pounds, down from 39 pounds. (Reporting by Nao Nakanishi, Editing by Peter Blackburn)