The London Aquarium is to undergo a £5m refurbishment.

The works, which are expected to be completed without one day of closure, will include the introduction of new walk-through tunnels, while the number of species will be increased from 400 to 500.

The attractions giant Merlin Entertainments acquired the aquarium – located in the former County Hall – in May this year and said that work will begin this month.

David Sharpe, divisional director of London Midway Attractions, which incorporates the London Aquarium, said: “In the current gloomy economic climate, our investment in the London Aquarium reflects the increased visitor numbers we have achieved since May and our absolute belief in the attraction’s potential.

“It is a wonderful space, in a great location on the Thames, and we have an expert team whose talents will be showcased by our new plans.”

The aquarium will be rebranded under Merlin’s Sea Life banner, but will keep its original name.

The work is expected to be completed by Easter next year.