* UK's total gas stocks high enough to meet 25 days of demand
* Spot gas prices down 30 pct since beginning of Ukraine crisis
* Forward prices down 12.5 pct during same time
LONDON, May 30 (Reuters) - British spot gas prices were trading at their lowest since October 2010 on Friday morning as healthy supplies clashed with low summer demand and high storage levels following a mild winter and spring.
Gas prices for delivery the next working day traded as low as 42.25 pence per therm on Friday morning, a third lower than they stood at the beginning of the Ukraine crisis in late February, and they are down over 40 percent since their winter peak last December.
"We're going into June now, so gas demand is approaching its annual lows during the summer. Even if Russia cuts gas to Ukraine now, it doesn't really matter in the shorter term, at least until the beginning of the winter heating season in October," one gas trader said.
Gas prices for delivery during the peak demand winter season, when an ongoing crisis between Russia, Ukraine and the European Union would hit markets more than during the summer lull, are down 12.5 percent since late February.
"The forward market is slightly more concerned about the situation in Ukraine than the spot market, hence winter prices didn't drop quite as sharply as spot prices, but even here supply looks pretty relaxed as utilities in Europe are pretty well prepared," another trader said.
The natural gas crisis between Russia, Ukraine and the European Union is fast turning from being a crisis of supply to one of payment.
Ukraine's gas bill for supplies from Russia is over a billion dollars a month, and Moscow says Kiev already owes it more than $5 billion for unpaid supplies, equivalent to around 3 percent of Ukraine's GDP.
Russia's Gazprom has threatened to cut off supplies to Ukraine in June if it does not receive at least some of its unpaid bills or an advance payment for future supplies from Ukraine.
Delaying an agreement will make it increasingly difficult for already cash starved Kiev to meet its obligations.
While the gas debt crisis becomes more accute, the supply situation eases the further Europe moves into the warm summer months.
Russia meets around a third of Europe's gas demand and sends almost half of this via Ukraine.
When Russia previously cut exports over pricing disputes with Kiev in 2006 and 2009, this happened during times of peak demand in winter, causing shortages and freezing across Europe.
But following a mild winter and spring as well as healthy supplies from non-Russian gas sources such as pipeline imports from Norway or liquefied natural gas (LNG) tankers from Qatar, Europe's gas storage sites are well filled this year and demand is very low as the region enters summer, the season with the lowest demand.
Five LNG tankers are scheduled to arrive in Britain during the next week, adding which together carry enough gas to meet 3.5 day's worth of current British gas demand, adding to the same amount already stored in Britain's LNG storage sites.
The week's worth of LNG supplies available to Britain adds to conventional natural gas from pipeline imports and domestic production that worth around 19 days' worth of current demand already in storage.
"All in all, we have enough gas in storage to meet 25 days of demand, and that's the best I can remember over the past five years or so," one gas analyst said
"Even if Russia cuts supplies, our storage combined with LNG imports and North Sea supplies from Britain, Norway and the Netherlands should be enough to get by for quite some time," he added. (Reporting by Henning Gloystein, editing by William Hardy)