Drilling the well, which will reach a depth of about 400 metres in Windsor Home Park, is expected to take about eight weeks. The Queen has already consented to the application from Canuk Exploration, a small oil company.
John Maisey, the councillor who proposed the plan be rejected at a meeting of Berkshire's development committee, said he feared for the future if Canuk struck oil.
"If they find it, they will want to get it out," he said. "The time to see if there is oil there is in the middle of the next century. We don't need to violate this site."
Planning officers reassured members that any company seeking to exploit oil reserves would need further permission for extraction. Mark Balchin, one of the county's planning consultants, said there had been no individual representation about the proposal, either for or against.
The application was approved by nine votes to three although it was reported to the committee that the Royal Borough of Windsor and Maidenhead, the local district authority, was strongly opposed to the plans. Don Beer, the Labour chairman of the development committee, said he was happy with the decision and believed the peace of the park would be preserved even if Canuk did discover substantial quantities of oil or gas. He added that there was an eight-to-one chance that oil would be found.
"My understanding is that they can build a pipe up to four miles away and there are plenty of gravel pits and disposal sites where these things could be placed with not much harm at all," he said.
The proposed site of the well is about 600 metres south-east of Windsor Castle in a private. part of the park. Drilling will take place using a mobile rig mounted on a lorry.
Only the very top of the 24m drill would be visible to the public, whose nearest viewpoint was from a distance of 360m. When drilling was complete the site would be restored and the ground reinstated to grassland.
Commander Michael Porter, chairman of the Berkshire branch of he Council for the Protection of Rural England, said yesterday that he was horrified by the decision to grant permission.
"This is a very special landscape and it's absolutely naive to believe that you explore for oil and then turn down its exploitation," he said. "If oil is found, the economic pressures will be very strong indeed".