UK GAS-Within-day prices slip as supply outpaces demand

* Gas system oversupplied by 5.9 mcm

* Unplanned outage at Bacton Seal ends

LONDON, Aug 22 (Reuters) - Prompt British natural gas prices for immediate delivery fell on Monday as higher domestic production and imports from Norway led to an oversupplied system.

Gas for within-day delivery fetched 27.50 pence per therm at 0852 GMT, down 0.35 pence from the last settlement.

Britain's gas system was oversupplied by 5.9 million cubic metres/day (mcm), with demand forecast at 162.8 mcm and supply at 168.7 mcm, National Grid (LSE: NG.L - news) data showed.

Domestic gas supplies were buoyed by higher flows through Total (LSE: 524773.L - news) 's Bacton Seal gas terminal which came back online over the weekend following an unplanned outage.

"Despite being expected, the increase in UKCS (UK Continental Shelf) flows was uncertain and might not have been fully priced in, particularly the end of the unplanned outage at Bacton Seal which was announced several times but eventually postponed," carbon analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said in a research note.

Bacton Seal flows were over 10 mcm/ day on Monday morning, up from zero last week, National Grid data showed.

Meanwhile imports from Norway through the Langeled pipeline were around 17 mcm/day.

Gas prices on the curve edged higher.

The Winter 16 contract rose 0.40 pence to 42.20 pence per therm and the September contract was up 0.55 pence at 28.80 pence per therm.

In the Netherlands, the day-ahead gas price at the TTF hub was 0.17 euro higher at 10.75 euros per megawatt-hour (MWh).

In Europe's carbon market the front-year EU Allowance (EUA) price slipped 0.03 euro to 4.74 euros per tonne. (Reporting by Susanna Twidale; editing by Nina Chestney)