UK GAS-Prompt prices fall on oversupplied system

* Gas system oversupplied by 27.8 mcm

* UKCS flows up on reduced impact of Teesside maintenance

* North Morecambe outage ends

LONDON, June 22 (Reuters) - British spot gas prices fell on Monday morning as strong domestic output and solid supplies from Norway left the system oversupplied.

Prices for within-day delivery were 42.50 pence per therm at 0807 GMT, down 1.95 pence from their last settlement.

Gas for delivery on Tuesday was 0.90 pence lower at 42.60 pence per therm.

With supply flows at about 198.3 million cubic metres (mcm) per day on Monday and demand expected to be about 170.5 mcm, the system was 27.8 mcm oversupplied, National Grid (LSE: NG.L - news) data showed.

UK Continental shelf (UKCS) flows were up to 127 mcm/d partly due to reduced impact from maintenance at TGPP's Teesside gas processing plant, analysts at Thomson Reuters Point Carbon said.

"Flows into Teesside PX are 9 mcm/d this morning compared to 4 mcm/d on Friday. We might see slightly higher increase into Teesside PX tomorrow as the maintenance at Teesside Processing Plant should end completely," the analysts said.

Annual maintenance at Teesside reduced flows by 60 percent from June 7-22 and would reduce flows by 20 percent on June 22-23 the company said.

Norwegian imports via the Langeled pipeline were around 15 mcm/d on Monday morning, National Grid data showed, up from around 10 mcm/d on Sunday.

Langeled is Britain's main sub-sea gas import route.

An unplanned outage at Centrica (LSE: CNA.L - news) 's North Morecambe (Barrow) gas sub-terminal in Britain ended over the weekend, Centrica said in a market update.

The outage cut capacity to zero from 0630 GMT on June 19 to 0222 GMT on June 20.

Gas prices further along the curve edged lower, with the July contract down 0.45 pence at 42.10 pence per therm.

In the Netherlands, the day-ahead gas price at the TTF hub was 0.23 euros lower at 20.40 euros per megawatt-hour.

Europe's benchmark front-year carbon price was up 0.05 euros to 7.49 euros per tonne on ICE Futures Europe. (Reporting by Susanna Twidale; editing by Jason Neely)