A judge on Monday ruled that the businessman who admired Margaret Thatcher so much leaving his millions to her Conservative Party was not of sound mind when he made the bequest.

According to High Court judge Launcelot Henderson Branislav Kostic was mentally ill when he left the party more than USD16.3 million, considered as one of the largest individual political donations in British history.

The judge added Kostic was "wholly unable to dispose of his property in the way he would have done if of sound mind."

With his ruling, an earlier will executed by Kostic leaving his fortune to his son Zoran should prevail.

Lawyers for his family argued at London's High Court that Belgrade-born Kostic, who made a fortune trading in pharmaceutical products and precious metals, was "deluded and insane" when he drew up a will leaving the money to the Conservatives.

Kostic died in October 2005 at the age of 80.