UK GAS-Prices rise as supply tightens

* Within-day gas up 1.18 pence at 34.03 p/therm

* Output cuts to tighten supply-demand balance

Aug 4 (Reuters) - British wholesale gas prices rose on Thursday as maintenance on the UK Continental Shelf tightened output and Norway scaled back deliveries.

Day-ahead gas rose by 0.80 pence to 34.10 pence per therm at 0946 GMT from the previous settlement, while gas for immediate delivery rose 1.18 pence or 3.59 percent to 34.03 pence per therm.

Although the UK gas system is currently oversupplied, analysts said flow data forecasts raise the possibility of shortfalls by market close, prompting traders to bid higher on prompt contracts.

Output from the UK Continental Shelf (UKCS) lowered again on Thursday to 105 million cubic metres/day (mcm) from 116 mcm/day on Wednesday and 132 mcm/day on Tuesday.

That reflects maintenance-related outages affecting the Bacton Seal terminal and the Britannia gas field.

"Prompt prices have opened the session higher, in line with lower supplies, with an extension to a current field outage in Norway adding to support," Wingas UK head of trading Marcel Boonaert said.

In Norway, Britain's biggest gas supplier, flows through the Langeled pipeline fell to 12 mcm/day from 19 mcm/day in the previous session.

On Friday Norway's other export pipeline to Britain, Vesterled, will have its capacity reduced by 24 mcm/day - although this may not curb actual Norwegian imports, analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said.

For the time being, Britain's gas market was oversupplied by 49.2 mcm/day with demand estimated at 157.9 mcm/day. However, that surplus - partly driven by ongoing withdrawals from storage - may be eroded later in the day, the analysts added.

In the Netherlands, the day-ahead price at the TTF hub was up 0.23 euro at 13.38 euros per megawatt-hour.

In Europe's carbon market, the front-year EU allowance price lost 0.43 euro to trade at 4.62 euros per tonne. (Reporting by Oleg Vukmanovic in Milan, editing by Nina Chestney)