One of the two cable braces supporting the tree failed and a large crack appeared in the trunk. A green oak A-frame has been used to give each beam extra stability. The tree crown is also supported by props and is now stable.
The council's parks horticultural service manager Richard Ennion said: "The Domesday Oak is one of the country's most famous trees and thanks to our partnership with Westwind Oak we were able to respond quickly. It is good to know the tree is saved for future generations."