High Court judge Mr Justice Peter Smith awarded the multi-millionaire nine per cent of the near £7m income from the tiny field since 2000 and the same percentage of future income.

The judge had heard that owners of the wells at Oxted, Surrey, did not tell Mr al-Fayed what was happening beneath his Barrow Green Court and Barrow Green Farm.

The case related to the Palmers Wood oilfield, where three wells were drilled diagonally and pass under the Oxted estate at a depth of at least 800ft. Mr al-Fayed sued the present owner of the wells, Star Energy, through his company Bocardo, claiming 12.5 per cent of the income.

Mr Justice Smith said in a ruling yesterday: "Bocardo claims that the laying of the pipes underneath the surface of the Oxted estate is a trespass.

"It can have no claim to the oil itself because the title to the oil is vested in the Crown."

His award was for trespass.

"Merely because it is measured by reference to a percentage of the income received does not make it a royalty in my view," said the judge.

The wells penetrate up to 700 metres under the Oxted estate to extract oil and gas.

Production began in October 1990 and initially the wells were producing 9,000 barrels a month but the rate had now reduced to 2,000 barrels, said the judge.

The total amount extracted by the end of 2007 was about 1,006,000 barrels worth £10m.

"There was nothing to indicate to Bocardo at the time that the wells were drilled that drilling had taken place under the Oxted estate and that oil was being extracted from under the estate via their wells," said Mr Justice Smith.

When Mr al-Fayed noticed the oil rig next to his estate in 1992 he instructed solicitors to find out "what actually was occurring", said the judge.

But they were told by the oil company that it could not reveal whether the borehole passed under the estate for "reasons of commercial confidentiality".

The judge accepted that the oil company was trying to avoid "revealing the true facts, namely that drilling was not only taking place under the Oxted estate but had already been happening for two years".

"The defendants were... perpetuating a decision not to tell Mr al-Fayed/Bocardo what was actually happening beneath the Oxted estate."

The judge rejected the oil company's argument that because there was no disturbance on the surface the activities did not cause any trespass.