Grimsby Dock Tower, Grimsby, Lincolnshire

Completed in 1852 at a staggering 309ft, the purpose of the Grimsby Dock Tower was to provide hydraulic power to the lock gates and cranes of Grimsby Docks. It contained a 30,000 gallon hydraulic wrought iron reservoir at a height of 200 feet to supply the pressure required.
The bricks from which the building is constructed were manufactured on the site and the clay dug from local marshes. At the time of its construction it was the highest building in Lincolnshire and the tallest brick-built building in the country.
And no, it's not in use today. Seemly the cost of demolition is pretty much all that's keeping it upright.