UK GAS-Within-day prices steady, day-ahead firm on FLAGS maintenance

* Gas system oversupplied by 5 mcm

* Langeled flows surge to 74 mcm/day

* FLAGS pipeline in maintenance on Monday

Feb 5 (Reuters) - British within-day gas prices were broadly steady on Friday as higher supplies from Norway offset lower deliveries from the UK continental shelf, while the day-ahead contract firmed on an expected drop in flows due to planned pipeline maintenance.

Gas for immediate delivery rose 0.05 pence or 0.17 percent to 28.65 pence per therm by around 1030 GMT, while the day-ahead contract for Monday gained 0.25 pence or 0.87 percent to 28.85 pence/therm.

Britain's gas system was oversupplied by 5 million cubic metres (mcm) on Friday morning, with demand forecast at 261 mcm, well below the seasonal norm of 283 mcm, and flows at 266 mcm/day, National Grid (LSE: NG.L - news) data showed.

Higher deliveries from Norway and low demand were the main reasons for the over-supply, analysts said.

Flows through the Langeled pipeline, Britain's main sub-sea gas route, surged to 74 mcm/day, with Norway's total deliveries to Europe rising to the highest levels since the start of 2012.

"Norwegian production is up, despite low demand in the UK and the Continent. It (Other OTC: ITGL - news) may be that production is up to compensate for lower FLAGS flows next Monday," said Oliver Sanderson, a gas market analyst at Thomson Reuters (Dusseldorf: TOC.DU - news) .

Norwegian flows through the FLAGS pipeline are expected to drop by 18 million cubic metres (mcm) per day on Monday due to planned maintenance.

Flows at Britain's Teesside gas processing plant, which has capacity to process about 19 million cubic metres of gas per day, were cut by 19 percent on Feb. 5-7, its operator said.

Supply from liquefied natural gas terminals remained strong, nominated at around 46 mcm/day on Friday, partly offsetting lower flows at Bacton Shell, Sanderson added.

Temperatures in Britain were forecast to be near or slightly above normal levels during most of February, but it may become generally colder for a time later next week, especially in northern and central areas, Britain's Met Office said.

Further along the curve, contract for gas delivery next-season, was trading at 27.60 pence/therm, 0.12 pence down.

In the Netherlands, the day-ahead gas price at the TTF hub fell 0.32 euro or 2.57 percent at 12.13 euro/MWh.

European carbon front-year allowances eased 0.04 euro to 5.58 euro a tonne. (Reporting by Nerijus Adomaitis in Oslo; Editing by Adrian Croft)