Equipment lies next to a shipping container housing exploratory well-head at Horse Hill, in Surrey, southern England on April 9, 2015. Reuters/Peter Nicholls

(Reuters) - The small British oil firm that caused a commotion in the media when it said it had found a possible world class oil resource in the southern English countryside, conceded on Wednesday that it was not in a position to properly size it up.

Headlines like "Britain's Dallas" featured in the national press last week when Explorer UK Oil & Gas Investments (UKOG) said last week that up to 100 billion barrels of oil could lie below the green fields around Gatwick Airport.

UKOG, whose shares soared 200 percent in the wake of the news, said in a "clarification of press comment" on Wednesday that its exploration related only to its license. The overall forecast of 100 billion barrels appeared to have been an estimate for the whole Weald Basin area.

"The company has not undertaken work outside of its license areas sufficient to comment on the possible oil in place in the whole of the Weald Basin," it said.

Industry analysts had last week received UKOG's news with a note of caution, pointing out that Kuwait's proved reserves amount to 101.5 billion barrels, according to BP's annual statistics, while Britain has extracted 45 billion barrels from the North Sea since the 1970s.

In its original statement, UKOG had already cautioned that only between 3 and 15 percent of the oil on its license could be recovered.

UKOG is the main investor in the Horse Hill project, while other stakeholders include Stellar Resources, Solo Oil and Alba Mineral Resources.