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UK GAS-Prices slide on supply surge as Norway outages end

* Gas grid oversupplied by 30 mcm/day

* Upcoming gas pipeline maintenance weighs on prices

June 14 (Reuters) - British wholesale gas prices extended losses on Tuesday morning as outages in Norway which had reduced flows ended and domestic output rose.

The price of gas for day-ahead delivery fell by 0.90 pence to 32.00 pence per therm by 0920 GMT, while gas for instant delivery fell 0.50 p to 31.90 p/therm.

Gas deliveries from Norway through the Langeled pipeline rose to 70 mcm/day, near maximum levels and a rarity during summer months when flows tend to taper off as demand slows.

The end of maintenance at Norway's Kvitebjorn and Gullfaks fields boosted output.

Analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said Norwegian production and exports via Langeled could fall in the coming days as UK gas prices decline in response to the Interconnector shutdown.

National Grid (LSE: NG.L - news) data showed demand was estimated at 189.1 mcm and flows at 219.3 mcm on the back of rising Norwegian supply.

"The system has again opened significantly long, with continued near capacity flows through Langeled after the resolution of unplanned outages leaving a 30 mcm surplus of gas on the system," said Marcel Boonaert, head of trading and portfolio at Wingas UK.

Domestic output from British fields also rose following the ramp-up of the Bacton Seal terminal over the course of Monday, after Total E&P UK fixed an offshore supply issues.

From Wednesday the Britain-Belgium Interconnector, an undersea gas pipeline, will shut for annual maintenance until June 30.

Britain uses the Interconnector to export gas to the continent when prices in Belgium are higher. Its shutdown potentially traps excess supply in the UK and removes an outlet.

"However, flows via (Britain-Belgium Interconnector) have already fallen to near zero from the beginning of June, meaning that the maintenance will not have a large impact on regional balances," according to consultancy Energy Aspects.

Temperature forecasts for the next two weeks also indicate a warmer-than-normal trend, reducing demand.

Further along the curve, gas for winter delivery fell 0.50 pence to 38.65 p/therm.

In the Netherlands, the day-ahead gas price at the TTF hub was down 0.13 euro at 13.65 euros per megawatt hour.

European front-year carbon allowances were down 0.06 euro at 5.80 euros a tonne. (Reporting by Oleg Vukmanovic, editing by Nina Chestney)