* Cold start to year boosts need for gas in heating systems
* Storage sites close to running out of gas in March, April
LONDON, May 30 (Reuters) - Britain's net gas imports rose to the highest ever level in the first quarter, government data showed on Thursday, underscoring the country's growing dependence on non-domestic gas supply.
Net imports climbed to 14.7 billion cubic metres (bcm) between January and March, up 21 percent from the same time last year, as an unseasonably cold start to the year boosted the need for gas in heating systems.
"This year's cold winter meant that gas demand was higher than in recent years and with domestic gas production declining the UK needed to import more gas," a spokesman for the Department of Energy and Climate Change said.
Britain's local gas output has been falling steadily since the mid-2000s as fields run out of reserves, forcing the market to step up imports from neighbouring countries like Norway and from liquefied natural gas (LNG) producers like Qatar.
Outright gas imports rose to 16.7 bcm in the first quarter, the highest since late 2010, while export levels fell to the lowest since the first quarter of 2008 to 2 bcm, the government data showed.
Unusually cold weather in March and April meant Britain's gas storage facilities were close to running out of stock, leaving Britain more dependent than ever on imports.
The country is trying to diversify its gas portfolio. Its biggest domestic gas supplier, Centrica, was one of the first companies globally to sign a U.S. LNG import agreement in March and the government has held energy talks with gas-rich Algeria.
It is also counting on the contribution of shale gas resources to soften Britain's dependence on imports.