UK GAS-Spot price edges up on disruptions to supply

* Outage at Kollsnes duration unknown

* Maintenance due to end at St Fergus

* System long 2 mcm

LONDON, Sept 22 (Reuters) - British spot gas prices firmed on Tuesday, supported by disrupted flows at Norway's Kollsnes gas processing plant and Vesterled's St Fergus terminal.

The outage at Kollsnes, which started on Monday, has reduced flows by 7 million cubic metres (mcm) per day and its duration was unknown, operator GASSCO said, while flows from Vesterled's St Fergus terminal are forecast to pick up, with maintenance expected to end Tuesday.

Gas for within-day delivery was up 0.1 pence at 40.80 pence per therm, while prices for day-ahead delivery were up 0.1 pence at 40.65 pence/therm at 0957 GMT.

The system was near balanced, with supply flows forecast at around 210 mcm, while demand was expected at 208 mcm, leaving the system long by 2 mcm, National Grid (LSE: NG.L - news) data showed.

Norway's Langeled pipeline flows were around 46 mcm/day, down slightly from the previous day.

"A switch to net (storage) withdrawals is required to balance the UK market," analysts at Thomson Reuters Point Carbon said in a morning note.

The analysts said that current UK gas prices could help encourage switching away from coal and into gas.

"If the current price level continues we could see additional demand from the power sector over the next two weeks," the note added.

The benchmark winter gas price rose 0.14 pence to 42.75 pence/therm.

In the Netherlands, the day-ahead gas price at the TTF hub was down 0.05 euros at 18.95 euros per megawatt-hour.

The benchmark European Union carbon price edged up 0.03 euros to 8.02 euros a tonne on ICE Futures Europe. (Reporting by Sarah McFarlane; Editing by Louise Heavens)