UK GAS-Prices fall as LNG supplies offset lower Norwegian imports

* Britain's gas market oversupplied by 11.2 mcm

* Four LNG tankers expected over the next 7 days

LONDON, Aug 18 (Reuters) - Prompt natural gas prices in Britain fell on Tuesday morning as supply outstripped demand and arrivals of liquefied natural gas (LNG) offset lower imports from Norway.

Prices for within-day delivery were trading at 39.60 pence per therm at 0812 GMT, down 1 pence since their last settlement.

The day-ahead contract traded at 39.50 pence per therm, down 0.66 pence on Monday's close.

With supply flows at about 194.2 million cubic metres (mcm) per day and demand expected to be about 183 mcm, the system was 11.2 mcm oversupplied, National Grid (LSE: NG.L - news) data showed.

Flows from the South Hook LNG terminal were around 60 mcm/ day on Tuesday morning, National Grid data showed, up from around 40 mcm earlier in the week.

LNG supplies are expected to remain high this week with four tankers due to arrive in Britain over the next seven days.

Analysts at Thomson Reuters Point Carbon said domestic gas supplies from the UK Continental shelf (UKSC) also rose on Tuesday, contributing to the oversupply.

Flows from the Easington Dimlington gas terminal, which processes UKCS gas, were around 6 mcm/day, up from zero on Monday morning, National Grid data showed.

Higher LNG and UKCS supply helped to offset reduced supplies from Norway.

Annual maintenance is expected to cut output from Norway's Kollsnes gas processing plant by 38.5 mcm/day Aug. 17-Aug. 27, operator Gassco said.

An unplanned outage at Norway's largest gas field Troll gas field will cut capacity by 16.2 mcm on Tuesday.

Prices were also lower on the Dutch TTF gas market where Day-ahead TTF gas was down 0.17 euros at 19.33 euros per megawatt hour.

In Europe's carbon market, benchmark EU Allowances (EUA) were down 0.04 euros at 8.21 euros per tonne. (Reporting by Susanna Twidale; editing by Jason Neely)