The total cost of the project now stands at �24m

The landmark, intended to open as part of the South coast's millennium celebrations, will now take another four months to finish.

The completion date has been changed from 5 January to the end of May 2005.

But the costs associated with the delay are still being assessed and will not be finalised until the end of September, the city council have said.

Speaking to BBC News Online Julia Brown, council spokesperson, confirmed the cost of the project now stands at �24m, about �10m over budget.

Project manager for the Spinnaker Tower, David Greenhalgh, said: "We are obviously disappointed that the completion date has slipped to May 2005.

"We will be spending the next few weeks looking closely at this new schedule with tower builders Mowlem to see if there is any scope for them to bring the date forward."

Built on Gunwharf Quays, near Portsmouth Harbour station, the Spinnaker Tower was first approved by the Millennium Commission in 1995.