When Portsmouth’s 550ft tall Spinnaker Tower opened last October, it was five years late and had cost £39.1m, nearly four times the original estimate. Critical opinion was divided over whether it was a magnificent monument or simply a monstrous waste of taxpayers’ money.

One year on, however, and the towering landmark seems to have established itself as a huge success, bringing thousands of international visitors and an estimated £10m into the city and its economy.

As the sail-shaped harbourside icon prepares to celebrate its first birthday tomorrow, almost 600,000 paying visitors have gone to the top, exceeding all forecasts and putting it firmly in the premier league of UK tourist attractions along with the London Eye and the Eden Project in Cornwall.

The runaway success of the first year even means the city’s taxpayers are finally getting some of their money back after seeing huge swathes of public cash poured in to keep the project afloat. Visitors have paid an average £5 each to go up the tower, spending £3m for the privilege, but there has also been a huge spin-off for the city’s other attractions; Jackie Shaw at the Historic Dockyard said that they’d had an extra 30,000 visitors since the tower opened. An economic study for VisitBritain estimates that the economic benefit to Portsmouth is about £10m.