The High Court agreed to alter the terms of a will so that the inheritance - which also includes a �250,000 annual income - will now pass to Earl Percy when he turns 25.

Edward Davidson, QC, representing the duke, told the High Court that the money could make Earl Percy, 14, vulnerable to "vices and pitfalls".

Mr Davidson pointed to the case of the Marquess of Bristol, whose death in January has been attributed to the playboy lifestyle he adopted after inheriting a large fortune aged 21.

The duke himself lost his older brother to drug abuse in 1995.

Kidnap dangers

Duke of Northumberland: "Not a heavy-handed father"

Mr Davidson also argued that inheriting the money at such a young age would make the earl vulnerable to kidnappers and to "spongers" who seek out wealthy heirs via the Internet.

He argued that the duke had his son's best interests at heart: "This is not a case of a heavy-handed father being suspicious and making sure his son is kept in place."

The earl was one of 13 defendents named in the case - all minors and potential beneficiaries of the will - who were represented by their legal guardians and who did not oppose the action.

Among them was the duke's younger son, Max, 8.

The fortune which Earl Percy stands to inherit comes from a trust fund set up in 1918 by the seventh Duke of Northumberland, benefiting from property in Surrey.