An exploration firm has announced the discovery of billions of barrels of oil reserves at a site near Gatwick airport.

UK Oil & Gas Investments (UKOG) said drilling of the 55-square mile site at the Weald Basin had discovered 158 million barrels per square mile.

Chief executive Stephen Sanderson said the Horse Hill-1 well required appraisal and testing to prove its commercial viability but that it had "the potential for significant daily oil production".

Together with another discovery, Portland Sandstone, it was a "possible world class potential resource".

Mr Sanderson told the BBC: "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."

Similar wells in the US had seen "estimated recovery factors" of between 3% and 15% of the oil in place, he added.

He said: "Drilling the deepest well in the basin in 30 years, together with the ability to use concepts, techniques and technology unavailable in the 1980s, has provided new cutting-edge data and interpretations to comprehensively change the understanding of the area's potential oil resources."

UKOG has an interest of just over a fifth in the Horse Hill site. Shares in the company initially more than quadrupled in value on the announcement.