UK GAS-Rally continues on Russian gas concerns, cold

* Day-ahead gas price rises almost 2 pence, March by 1.25 pence

* Temperatures seen dropping below normal at beginning of March

Feb 26 (Reuters) - British gas prices rallied for a third straight session on Thursday on concerns about Russian gas supplies to Europe via Ukraine and an expected drop in temperatures in March.

Gas prices for day-ahead delivery rose by 1.95 pence per therm to 53.45 pence by 0900 GMT, while prices for within-day delivery were up 1.9 pence at 53.30 pence/therm.

"The main issue is Russian gas supplies via Ukraine. If that doesn't get solved within a couple of days, the market will rally further," a UK gas trader said.

President Vladimir Putin warned on Wednesday that Russia would halt gas supplies to Ukraine if it did not receive advance payment, raising the possibility of onward deliveries to Europe being disrupted for the fourth time in a decade.

"Any new development of this dispute today is likely to be the dominant driver for European gas prices," analysts at Thomson Reuters Point Carbon wrote.

Europe gets around a third of its gas from Russia, with roughly half pumped via Ukraine.

The month-ahead March gas contract firmed by 1.25 pence to 53.30 pence per therm.

Traders also said the colder outlook was supporting prices, despite an oversupplied gas system, as temperatures are forecast to fall below normal at the beginning of March.

National Grid (LSE: NG.L - news) data showed physical gas flows into the country's transmission system at 275.8 million cubic metres (mcm) by around 0900 GMT, above estimated demand of 267.5 mcm.

Norwegian gas flows to Britain edged higher on stronger flows via the Vesterled pipeline, while there were three LNG cargoes scheduled to arrive at the end of February and the beginning of March.

Britain's Teesside gas-processing plant was experiencing an upstream flow reduction of 100 percent on Thursday, with the outage expected to last six hours, its operator TGPP Ltd said.

Some traders said they expected more LNG than scheduled as a 60 percent drop in Asian prices in the past year, driven by a streak of mild weather and new supplies, has made Europe the most attractive market for flexible cargoes.

Further out on the curve, the summer contract was up 0.95 pence at 48.25 pence/therm.

In the Netherlands, the day-ahead gas price at the TTF hub rose by 89 cents to 24.02 euros per megawatt-hour, tracking the rises in British gas.

In Europe's carbon market, benchmark EU allowances eased 6 cents to 7.39 euros a tonne. (Reporting by Nerijus Adomaitis in Oslo; Editing by Dale Hudson)