UK GAS-Prices rise as Ukraine gas transit risks resurface

* Gazprom warns of 'serious' risks to gas transit

* Norwegian gas flows via Vesterled fall to zero (Updates with Vesterled flows to UK falling to zero; updates prices)

LONDON, Feb 24 (Reuters) - British natural gas prices rose on Tuesday as Russia's Gazprom warned of "serious" risks to gas transit to Europe via Ukraine after Kiev failed to make a pre-payment and as Norwegian gas flows through the Vesterled pipeline fell to zero.

Prices for day-ahead delivery rose by 1.75 pence or 3.59 percent from the previous settlement to 50.50 pence per therm at 1043 GM (NYSE: GM - news)

The within-day contract was 1.10 pence or 2.24 percent higher at 50.20 pence per therm.

Further along the curve, gas for March delivery was 2.10 pence or 4.38 percent higher at 50.00 pence per therm.

"News that Russia might stop gas deliveries to Ukraine has helped push prices up," a gas trader said.

Gazprom said on Tuesday that Ukraine had 219 million cubic metres (mcm) of gas left, enough for two days. With no new payment, Russia would be forced to stop supplies to Ukraine, the company added.

Europe gets around a third of its gas from Russia, with roughly half being pumped via Ukraine. Britain imports around 15 percent of its gas demand from continental Europe, and a large portion of this volume will have originally been imported from Russia.

Norwegian gas flows to Britain via the Vesterled pipeline also fell to zero after 0940 GMT on Tuesday, Gassco data showed. The flows were running at around 18 million cubic metres (mcm) per day before the drop.

Gassco was not immediately available to comment.

As a result, Britain's gas system was largely balanced after being oversupplied in earlier trade, according to National Grid (LSE: NG.L - news) .

In the Netherlands, day-ahead gas price at the TTF hub was 0.75 euros higher at 22.70 euros per megawatt-hour, tracking the rises in British gas.

Consumption by households, services and small industry in the Netherlands, Germany, Belgium and France was forecast to surge by 253 gigawatt hours per day on Wednesday to 6,499 GWh/day, according to Thomson Reuters Point Carbon data.

The data also showed that Russian gas flows through the German Mallnow compressor station, which handles mainly Russian gas for transportation to western Germany, decreased to 747 GWh on Tuesday from 784 GWh earlier in the morning.

In Europe's carbon market, benchmark EU Allowances fell by 0.09 euros to 7.67 euros a tonne. Members of the European Parliament are due to vote on early reform of the emissions trading scheme at around 1400 GMT on Tuesday.

(Reporting by Nina Chestney; Editing by Liisa Tuhkanen and Louise Heavens)