UK GAS-Prompt prices slip as strong supply trumps higher demand

* Gas system oversupplied by 10.7 mcm

* Demand around 9 pct up on seasonal norm

LONDON, Dec 3 (Reuters) - Prompt natural gas prices in Britain fell on Wednesday as strong flows from Norway and an increase in supply from the Isle of Grain liquefied natural gas (LNG) terminal outpaced a rise in demand.

Gas for within-day delivery traded at 56.20 pence per therm at 0900 GMT, down 0.53 pence since the last settlement. Prices for delivery on Thursday were down 0.50 pence at 56.35 pence per therm.

Wednesday's demand was around 9 percent above the seasonal norm of 276 million cubic metres (mcm), National Grid (LSE: NG.L - news) data showed, as cold weather, which also was forecast for Thursday, increased demand from power stations.

Solid (KOSDAQ: 050890.KQ - news) supply from Norway and the release of around 15 mcm of gas held in storage at the Isle of Grain LNG terminal led to an oversupplied system.

With supply flows at about 310.7 mcm per day on Wednesday and demand expected to be about 300 mcm, the system was 10.7 mcm oversupplied, National Grid data showed.

"Isle of Grain sendout is crucial to the movement of the DA (day-ahead) contract. With the terminal operator's likely marketing gas yesterday for delivery today, the DA price lost value despite rising consumption," analysts at Thomson Reuters Point Carbon said in a daily market report on Wednesday.

Gas flows from Norway's Langeled pipeline were expected at full capacity at around 70 mcm, National Grid data showed.

Forecasts from Britain's Met Office showed temperatures would fall from an average of around 6 degrees Celsius on Wednesday to 4.5 degrees on Thursday and just 3.5 degrees on Friday.

Further along the curve, gas for delivery in Q1 2015 was 1.15 pence lower at 51.90 pence per therm.

In the Netherlands, the day-ahead gas price at the TTF hub was 0.17 euros lower at 23.50 euros per megawatt-hour (MWh).

The benchmark European Union carbon price rose 0.02 euros to 6.87 euros a tonne on ICE Futures Europe. (Reporting by Susanna Twidale; editing by Jane Baird)