Portsmouth's troubled landmark Spinnaker Tower may not be ready in time for the city's Trafalgar anniversary festivities this summer.
The spire will bring the tower to its full height of 170m (557.7ft)
The tower - originally planned to be completed in time for the millennium - was to have played a major role in the 200th anniversary events.
But builders Mowlem said on Tuesday they would need another £2m to ensure it was ready in time.
Portsmouth Council has said it will not spend any more on the project.
The tower, which was to have been entirely privately funded, has cost taxpayers over £10m already.
Leader of Portsmouth City Council, Cllr Gerald Vernon-Jackson, said: "Yesterday, Portsmouth City Council considered an offer from the main contractor to the Spinnaker Tower, Mowlem, to guarantee early completion of the project for an increased cost.
Festival of the Sea
"A decision was made to reject this offer and continue with the project in accordance with the contract that is currently in place.
"It was agreed that the deal was not in the interests of the people of Portsmouth, which is why it was rejected.
"We look forward to continuing to work with Mowlem on this landmark project with a view to completion at the earliest possible opportunity."
Portsmouth is to host the summer-long International Festival of the Sea, which culminates in the Trafalgar celebrations.
Built on Gunwharf Quays, the Spinnaker Tower was first approved by the Millennium Commission in 1995 and has been beset by delays.