* Norway's biggest gas field back up after short outage
* Gas flows to UK via Langaled link inch higher after drop
(Recasts with ramp-up completed, details)
OSLO/LONDON, Jan 7 (Reuters) - Gas production returned to normal levels at Troll, Norway's biggest field, and operator Statoil described the supplies as "secure and reliable" after a several hour stoppage stoked alarm in Britain on Thursday.
Norwegian oil and gas producer Statoil said the ramp-up of gas production at Troll was completed in the afternoon hours after the field's A platform was shut for about two hours from about 0815 GMT on Thursday.
"Let me stress that Troll supplies are secure and reliable," Statoil spokesman Gisle Johanson said. "Troll is back up to normal levels."
Troll, which can supply more than 10 percent of Britain's peak winter gas demand, as well as ship heating fuel to continental Europe, also shut because of a leak on Sunday, contributing to a surge in gas prices as freezing weather gripped northern Europe. [ID:nNWLA1862]
Johanson said the two outages were not related, as some gas market traders had suspected amid run-away speculation about the impact of any longer-term problems at Troll given Britain's record gas demand during the ongoing cold spell.
"It is unfortunate that these incidents happened one just after another. As always, we are doing our best to avoid similar situations in the future," Johanson said of the Troll outages.
Thursday's shutdown came as freezing temperatures have driven British gas demand to record highs, testing the country's gas supplies all week and triggering two rare gas supply alerts.
Data from UK gas network operator National Grid showed input from Norway via the Langeled pipeline dived from about 70 million cubic metres to 25 mcm/day at around 1110 GMT on Thursday, three hours after the shutdown, leaving the network short of gas and driving up spot prices in Europe's biggest gas market. At 1712 GMT flows rose to around 35 mcm/day.
Discovered in 1979, Troll still has an estimated 995 billion standard cubic metres of recoverable gas reserves after early production focused on oil.
Statoil has a 30.6 percent stake in Troll and is the field operator. Norway's state-owned Petoro has 56 percent, Shell (RDSa.L) has 8.1 percent, France's Total (TOTF.PA) 3.7 percent and U.S> ConocoPhillips (COP.N) 1.6 percent.
(Additional reporting by Kwok W. Wan, editing by Keiron Henderson)