UK GAS-Prices fall on oversupply, cancelled Norway maintenance

* Norway cancels major planned production maintenance

* Weak oil prices weigh on curve contracts

Aug 2 (Reuters) - British gas prices mostly fell on Tuesday as supply outstripped demand and Norway's cancellation of a major planned production outage helped ensure steady imports over coming days.

Gas for immediate delivery was flat at 34.20 pence per therm.

Although the day-ahead rose 0.65 pence to 34.80 pence per therm, all other contracts across the forward curve fell in response to continuing weak crude oil prices and ample supply.

Real-time flow data from network manager National Grid (LSE: NG.L - news) remains unavailable due to a technical glitch on Monday, reducing trading liquidity as a result of less visibility.

"The system is currently forecast to close the session 13 million cubic metres/day (mcm) long, with total demand in line with seasonal normal levels at 172 mcm," Wingas UK head of trading Marcel Boonaert said.

Norwegian supplies through the main Langeled import pipeline are seen higher at 22 mcm/day, although greater exports through the Britain-Belgium pipeline should offset that, he added.

Norwegian gas grid operator Gassco cancelled a planned 30 mcm/day supply outage due to begin on Wednesday.

UK Continental Shelf gas flows are 6 mcm/day higher at 136 mcm/day mainly due to increased deliveries to Bacton terminals, analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said.

Maintenance at the Britannia gasfield is scheduled to start at 1500 GMT to Aug. 18, although flows into the St Fergus Mobil terminal already dropped as of Monday in anticipation of the shutdown -- down to 10 mcm/day from 18 mcm/day.

The Bacton SEAL pipeline system will also start maintenance from Aug. 3-7 and flows may remain depressed thereafter, Thomson Reuters analysts said.

Gas prices for September fell 0.06 pence to 35.92 pence per therm and October levels declined 0.25 pence to 37.20 pence per therm.

Further along the curve, the benchmark winter 2016 contract fell 0.30 pence to 43.25 p/therm.

In the Netherlands, the day-ahead price at the TTF hub fell 0.07 euro to 13.58 euros per megawatt-hour.

In Europe's carbon market, the front-year EU allowance price was down 0.01 euro at 4.37 euros per tonne. (Reporting by Oleg Vukmanovic; editing by Louise Heavens)