Image caption At present there is little to see at Northern Petroleum's Markwells Wood facility

A £500m battle is welling up over a picture postcard piece of English countryside.

An area of ancient woodland in the rolling hills of the South Downs in West Sussex, Markwells Wood is a world away from rain-lashed oil rigs in the North Sea or sun-bleached oil refineries in the deserts of Saudi Arabia.

Yet hidden behind the trees is one of the UK's newest onshore oil wells.

With testing work continuing, the owner, London-based Northern Petroleum, estimates it could produce about five million barrels of oil.

This is tiny in comparison with reserves in the Middle East, but with the UK's offshore oil supplies in the North Sea running low, Northern's argument is that such small onshore oil fields - of which there are currently 28 scattered across Britain - together play a vital role in reducing our dependence upon imports.

'Hidden away'

As Derek Musgrove, Northern's managing director, drives up to Markwells Wood in his Land Rover, the only obvious sign it houses anything at all is a basic gravel access track.

"As you can see, the facility is very much hidden away," he says.

"The trees all the way around the site are not just a visual barrier, but excellent sound proofing - you would be surprised at just how effectively trees absorb noise."

At present all is quiet at Northern's site - two acres of levelled land cut from the wood, with the small wellhead roughly in the middle.

Beneath the flooring of basic compacted stone is a thick plastic membrane, which covers the entire site, including a trench running all the way around the perimeter.

"While it is highly unlikely that there will be any leaks, we don't take any chances, and the membrane is there for containment," says Mr Musgrove.

"Everything we do is about best environmental and safety practice. We wish to be the best possible neighbour, and behave with the utmost care."

'Natural beauty'

But while Northern Petroleum is keen to stress its environmental credentials, it has a fight on its hands to win planning permission to start actual production.

Markwells Wood is only going to produce a tiny amount of oil in the scheme of things, and it just isn't worth the potential environmental damage Richard George, Greenpeace

Especially as Markwells Wood, near Chichester, lies within the new South Downs National Park, which came into being on 1 April of this year.

Northern was granted planning permission in 2008 by West Sussex County Council, but only for exploration work.

It needs additional planning permission to start production, and now this decision will be in the hands of the new South Downs National Park Authority (SDNPA).

The authority does not appear favourable to the idea of a new oil well, saying it has two statutory purposes:

To conserve and enhance the natural beauty, wildlife and cultural heritage of the area

To promote opportunities for the understanding and enjoyment of the special qualities of the Park by the public

A SDNPA spokeswoman says: "All planning decisions within the South Downs National Park have to give effect to the twin purposes of the park.

"Major mineral development would only be considered acceptable in exceptional circumstances, and would need to be rigorously assessed in line with national policy."

'Conservation danger'

Northern also faces sizeable - and vocal - opposition from environmental groups.

Image caption Northern Petroleum's well is hidden away in Markwells Wood

Woodland Trust campaigns case officer Christine Byrne says: "We expressed our disappointment when it was first announced that Northern Petroleum would be drilling for oil [in Markwells Wood], and our view still stands that ancient woodland is irreplaceable.

"Furthermore we fear that the discovery of oil at Markwells Wood may mean that further testing or extraction is inevitable across the South Downs, spelling danger for other precious conservation sites."

Greenpeace climate campaigner Richard George says the South Downs National Park is "a beautiful area that we really don't want to be trashing to keep us hooked on oil".

He adds: "Instead of carte blanche to tear up the south of England, let's reduce our demand for oil.

"Markwells Wood is only going to produce a tiny amount of oil in the scheme of things, and it just isn't worth the potential environmental damage."

Image caption Northern Petroleum says it aims to be a good neighbour and consults with local people

If the national park authority does turn down its application, Northern would be able to appeal to the Planning Inspectorate, which deals with appeals in England on behalf of the Department for Communities and Local Government.

While the Planning Inspectorate decides on most appeals itself, for contentious issues the decision is left to the Communities Secretary, Eric Pickles.

In Northern's favour are three main factors.

UK onshore oil and gas industry Accounts for just 1.5% of total production. 98.5% being offshore

28 current onshore oil fields

Has been operating for more than 60 years

Oil wells in Nottinghamshire were vital for fuel supplies during World War II

The largest onshore oil field is Wytch Farm in Dorset

Firstly, it has a proven track record of stringent environmental standards at its existing onshore UK oil wells.

Secondly, another government department, the Department of Energy and Climate Change (DECC), is generally favourable to onshore oil and gas exploration, saying it contributes "usefully to UK security of supply and to the UK economy".

And more importantly, the DECC has already given Northern the government licences it needs - in addition to future planning permission - to start production at Markwells Wood.

Back at Markwells Wood, Derek Musgrove says he is happy to be patient.

"We never rush these things, and continue to consult locally," he says.