Animal welfare campaigners are pleading for the release of 15 penguins they say are "trapped in the basement without sunlight or fresh air' at London Aquarium.
A demonstration was held by Freedom For Animals with support from Born Free and The Express Newspaper with roughly 250 to 300 people protesting against the captivity of 15 gentoo penguins at the riverside attraction in Westminster.
The aquarium - owned by Merlin Entertainments - introduced penguins in 2011.
It brought over 10 gentoo penguins from Edinburgh Zoo.
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A Sea Life London Aquarium spokesman said the penguins' habitat was "designed to help and advice from specialist vets".
Campaigners say the penguins "have now endured 14 years in a basement" with only six to seven feet deep water.
Former Undertones singer Feargal Sharkey told Merlin Entertainments Chief Executive Fiona Eastwood to trade "places with the penguins".
"In fact, if she's prepared to actually spend a month down there with those penguins, I will donate £1,000 of my money to a charity of her choosing," he added.
Campaigners have said the penguins have endured 14 years in a basement
|PA
"There is no reason that they should be benefiting at all from imprisoning 15 birds in the basement of an old council building."
Mr Sharkey said it was "idiotic".
He added it was "nonsense, and it's got to stop".
Merlin Entertainments is co-run by a number of different companies.
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Hundreds of people attended a demonstration organised by Freedom for Animals at the aquarium
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The British theme park giant owns a number of attractions across the UK.
Those include Alton Towers, Legoland Windsor, Madame Tussauds, Thorpe Park, and Chessington World of Adventures.
A spokesman said the enclosure provided an "excellent balance of water and land for the penguins".
The spokesman added that it enables the penguins to express their normal behaviours and that there was space for them to ensure they had enough privacy.
Naturalist and TV presenter Chris Packham rejected the venue's claims.
He was in attendance at the demonstration and said it was a "blight on the reputation of London's attractions".
"I could get some specialist architects to build you and me a house in an asbestos factory - we wouldn't want to live in it, would we?" Mr Packham said.
Freedom For Animals launched its Free The Fifteen campaign in January last year.
It argued that ever since the gentoo penguins were not classified as an endangered species, there was no justification for breeding and keeping them in captivity.
Sea Life Aquariums counted more than 30,000 sea creatures across its 11 UK centres as of this year's stocktake.
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