The Grade I listed ancient monument, with magnificent views over the Humber, east of Hull, had no roof and no battlements before work began 15 months ago.
“We haven’t finished, but the building has been saved,” said owner Simon Taylor, adding that “sheer bloodymindedness” had kept him going through more constant vandal attacks and fruitless attempts to raise funds for the restoration works in recent years.
“Up till last year there were trees growing out of the top. Rainwater was washing out the mortar joints in the barrel vaulted ceiling downstairs and bricks were starting to fall out.
“If the ceiling had collapsed there would have been nothing left to save.”
Built in the Middle Ages by Robert Holme, a prosperous landowner, the tower is believed to have been originally one of two on either end of a manor house.
Without the battlements it looked “squat, odd”, said Mr Taylor, who bought the building, hoping to save it for posterity, in 1992. “Now it’s architecturally spot on,” he said.
Mr Taylor added: "For the last 25 years I've been looking at it and saying this building is fantastic - and everyone else was sniggering.
"English Heritage came up with the goods - it is absolutely brilliant.
"It is now restored to a state it hasn't been in for over 100 years."
The tower has 6ft thick walls and a portcullis - which allowed the family to withdraw to safety and shut the door when under attack from invaders coming up the river.
The rest of the buildings were demolished in the early 19th century and was converted into a gazebo or lookout in 1871.
Mr Taylor says there could be an opportunity now to convert the building into a house with a modern extension - even if he is not the person who does the project.