The London Aquarium is to be merged into the capital's premier group of tourist attractions, which already includes the London Eye, Madame Tussauds and the London Dungeon.

Merlin Entertainments is buying the Aquarium from the Japanese company that owns County Hall, the South Bank site of the old Greater London Council which is now a luxury four-star hotel.

Merlin is not saying how much it is paying Shirayama Shokusan for the 35-year lease on the business, but it is committing to a £5 million revamp of the attraction and special offers to visitors who want to fly the Eye next door or visit Merlin's other London attractions.

Merlin is backed by the financial might of US private-equity giant Blackstone and the Dubai Investment Corporation, recently linked to Liverpool FC.

The group's other attractions around the country include Legoland, Alton Towers, Thorpe Park, Chessington World of Adventures and the Sea Life aquariums chain.

Merlin director Glenn Earlam said it was the ability to cross-sell the Aquarium as part of a London package, as well as the group's Sea Life expertise, that drove the deal.

"It is an excellent attraction in an excellent location but we believe we can add a little Sea Life magic to it and make it more interactive with 'touch pools' for the children," he said. "There are also obvious economies of scale and marketing opportunities in having a 'city cluster' of attractions."

The Aquarium currently has 750,000 visitors a year, and Earlam believes those numbers are holding up.

"Despite what is happening elsewhere in the economy, London visitor numbers remain strong," he said.