An exploration firm has announced the discovery of billions of barrels of oil reserves at a site near Gatwick airport.
UK Oil & Gas Investments 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 Britain] 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.
The oil reserve is located to the north of Gatwick Airport (map: Google)
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.
UKOG has a 30% direct interest in operator Horse Hill Developments Ltd and a 1.32% interest via its holdings in another company, Angus Energy. HHDL owns a 65% interest in the licence for the well.
In a statement today, UKOG said that in order to establish estimates of total oil in place within the licence area, the "semi-regional resource potential of the Weald Basin's eastern footprint is the subject of ongoing analysis".
Mr Sanderson told the BBC: "Based on what we've found here, we're looking at between 50 and 100 billion barrels of oil in place in the ground.
"We believe we can recover between 5% and 15% of the oil in the ground, which by 2030 could mean that we produce 10%-to-30% of the UK's oil demand from within the Weald area."
UKOG chairman David Lenigas tweeted: "The Weald Basin is 1,110 sq miles and this discovery is very significant for UK. Very significant."
He told Sky News the discovery would mean "many thousands" of jobs.
It has previously been estimated that the Weald Basin holds 4.4 billion barrels.
The figures compare to offshore oil and gas production, primarily from the North Sea, which has seen 43 billion barrels extracted to date, according to the latest estimate from Oil & Gas UK, the trade body for the offshore sector.
It estimates that between 12 billion and 23 billion barrels are left.
Greenpeace UK chief scientist Dr Doug Parr said: "To gleefully rub your hands at a new fossil fuel discovery you need to turn the clock back to the 19th century and ignore everything we have learnt about climate change since.
"We already have more than enough coal, oil and gas reserves to fry the planet. Dotting the English countryside with drilling rigs and pipelines to squeeze the last drop of oil out of Britain doesn't make any sense.
"It's time we uncoupled our economy from the dangerous rollercoaster of fossil fuels and invested in the clean technologies that can provide safe and cheap energy for decades to come."
Friends of the Earth South East campaigner Brenda Pollack said: "The prospect of dirty oil extraction in southern England will greatly alarm local communities and put fracking firmly on the region's election agenda.
"Any firm proposing to drill for oil in the region knows it will face huge opposition - as happened at Balcombe, Fernhurst and Wisborough Green. Drilling proposals in Sussex have already been turned down.
"The next government must end our reliance on climate-changing fossil fuels and invest in real solutions to the energy challenges we face, such as renewable power and energy efficiency."