LONDON, June 20 (Reuters) - A local authority should

have considered the long-term climate impact of onshore oil

wells when it granted them planning permission, the UK Supreme

Court ruled on Thursday in a decision that could hugely impact

any future fossil fuel developments.

Environmental campaigners had argued that planning

permission for the retention and expansion of an oil well site

in southern England was flawed because it had only considered

the direct effect of the development, and not the impact of

greenhouse gas emissions from the use of the extracted oil.

Judges on the UK's top court agreed by a narrow three to two

majority, saying the planning approval was unlawful because the

later emissions should have been considered in an Environmental

Impact Assessment (EIA).

"It is not disputed that these emissions, which can easily

be quantified, will have a significant impact on climate," said

George Leggatt, one of the three Supreme Court justices who

agreed with the appeal.

"The only issue is whether the combustion emissions are

effects of the project at all. It seems to me plain that they

are."

Ahead of the ruling, campaigners said, if they won, the

landmark judgment would make it much harder for new oil, gas and

coal developments to get approval, and other controversial

schemes would be impacted.

"It is extremely difficult to overstate the significance of

this case," said Sam Fowles, planning and environment law

specialist at Cornerstone Barristers. "(It) could be the

beginning of the end of new fossil fuel extraction in the UK."

In 2019, Surrey County Council gave permission for Horse

Hill Developments, part owned by British energy company UK Oil &

Gas Plc, to retain two oil wells and drill four more over more

than 20 years near the town of Horley, close to London's Gatwick

Airport.

An EIA for the project examined the effect of the

construction, production and decommissioning of the site but did

not assess the downstream impact from emissions that would

result from the use of the oil when it was later refined and

used, for example as fuel.

The Weald Action Group (WAG), an umbrella organisation for

local groups that campaign against the extraction of oil and gas

in southeast England, estimated this would equate to more than

10 million tonnes of carbon emissions.

A campaigner acting for WAG launched a legal challenge

against the planning approval, but this was rejected both by the

High Court in London and then by the Court of Appeal which ruled

had the council had not acted unlawfully and that it was for

government to decide on the making of policy.

"In my view, there was no basis on which the council could

reasonably decide it was unnecessary to assess the combustion

emissions," Leggatt said in his Supreme Court judgment.