London (AFP) - An oil exploration firm said Thursday that it had discovered 100 billion barrels of oil in the ground next to Gatwick Airport outside London.

Although only between three and 15 percent of the total is likely to be extractable, UK Oil & Gas Investments (UKOG) said the Horse Hill well in Surrey, southwest England, was a "world class potential resource".

"We think we've found a very significant discovery here, probably the largest (onshore in the UK) in the last 30 years, and we think it has national significance," Stephen Sanderson, the firm's chief executive, told the BBC.

For a comparison, a total of around 42 billion barrels of oil have been extracted from the North Sea since the first licences were issued there in 1964.

UKOG said the controversial technique of fracking should not be necessary to extract oil from the 55-square-mile (88-square-kilometre) site in Surrey.

Its finding comes despite the British Geological Survey, a government organisation, reporting last year that the region may only have between 2.2 and 8.5 billion barrels of oil.

Industry body United Kingdom Onshore Oil and Gas (UKOOG) said more testing was needed to see how much of the oil could be extracted from the ground.

"These initial results suggest a very large volume of oil in place, which could potentially help to stem the rise in oil imports and improve Britainâs energy security and balance of payments," its chief executive Ken Cronin added.

Some 2,000 oil wells have been drilled in Britain since the 19th century and 250 are still operational, producing between 20,000 and 25,000 barrels of oil equivalent per day.