British spot gas prices shot to a 10-month high on Thursday morning as persisting cold weather pushed demand to almost 20 percent above the seasonal norm.

A Siberian cold front which has much of Europe in its grip meant that gas demand in the UK was expected to rise to over 400 million cubic metres (mcm) on Thursday, more than 18 percent above the seasonal norm of 331.1 mcm, National Grid data showed.

As a result, gas prices for within-day and for next-day delivery shot to levels last seen shortly after the Fukushima nuclear disaster in March 2011.

Within-day gas was trading at 64 pence per therm at 0900 GMT, and gas for delivery on Friday was around 64.80 pence.

Spot power prices also shot up, with baseload (24 hours) power for delivery on Friday rising 5 pounds per megawatt-hour (MWh) to 51.75 pounds a MWh.

Traders said the move was in line with rallies in the gas market and in continental Europe's power sector, where spot power prices hit their highest level since December 2010.

HEALTHY GAS FLOWS & STORAGE LEVELS

But despite the high demand, there was no supply shortage in the UK as Norwegian flows were healthy and suppliers increased withdrawals from their high storage levels.

National Grid data showed that Britain was expected to have 410 mcm of gas available on Thursday, which would leave the system over 5 mcm long.

The high prices are a risk premium, because whilst supplies are being covered at the moment, just one pipeline glitch would leave the system desperately short and would rapidly deplete storage at a time when nobody knows how long this cold is going to last, one gas trader said.

Point Carbon data showed that storage withdrawals had risen from around 40 mcm per day at the beginning of the year to almost 100 mcm at the beginning of February.

Because this is Europe's first cold snap in what has otherwise been an unusually mild winter, gas storage levels are still healthy.

Britain's gas storage sites were almost 73 percent full on Wednesday afternoon, compared with a European average of 65.17 percent, according to data from Gas Infrastructure Europe.

At this point last year, storage sites were filled to under 50 percent across Europe.

WEATHER

The UK's Met Office said that it expected cold weather to persist across Britain on Friday, but that slightly warmer temperatures with unsettled conditions were expected by the weekend.

But large parts of continental Europe are not expected to see milder weather by the weekend.

Meteoalarm, a European service to warn of extreme weather, had cold weather warnings in place for most parts of continental Europe, except for parts of Spain, Belgium, the Netherlands, and the Scandinavian countries. (http://www.meteoalarm.info/)

(Reporting by Henning Gloystein; editing by Keiron Henderson)