Drilling for oil is due to begin in the South Downs National Park.

Northern Petroleum was granted permission by West Sussex County Council to drill for oil in the ancient woodland at Markwells Wood, near Chichester, in January 2009.

The firm has now decided to start drilling for crude oil on the site, which has since been made part of the South Downs National Park.

The oil company plan to drill down to depths of up to 1,831 metres and believe there could be between 35 million and 61 million barrels of crude oil, worth $80, or almost £50 each, in the oil field beneath the South Downs.

At the time the application was first submitted, Natural England objected to the plans on the grounds that it could harm the habitat of protected species in the woodland.

They also called for a dormouse survey.

Derek Musgrove, managing director, of Northern Petroleum said: “The commercial case for drilling Markwells Wood is compelling when the price level of oil is above $80 per barrel.”

In May 2008 West Sussex County Council granted permission for the company to clear a hectare of the wood on South Holt Farm and use a 36m drill 24 hours a day to search for oil.