Twenty cross-party MPs have demanded the release of 15 penguins from a basement aquarium enclosure without daylight or fresh air.
All four Green Party MPs, Labour MP Mary Kelly Foy and 15 Liberal Democrats have signed an Early Day Motion (EDM) calling for Sea Life London Aquarium to free the gentoo penguins.
Isobel McNally, campaigns officer at Freedom for Animals, said: " "The fact that 20 of our MPs have now signed the EDM calling for an end to Sea Life and Merlin Entertainments' exploitation of gentoo penguins sends them a clear message: what you are doing is wrong, and people at every level want you to stop.
"Almost 2,500 members of the public have now signed the petition for their release. Enough is enough. Stop breeding more animals to be used as exhibits, and rehome those you already have to appropriate sanctuaries."
EDMs are motions submitted for debate in the House of Commons for which no day has been fixed.
By attracting the signatures of more MPs, the EDM can be used to demonstrate the level of parliamentary support for the campaign to free the penguins.
Very few EDMs actually get debated but they help draw attention to a topic.
Broadcaster Chris Packham, former Undertones frontman Feargal Sharkey and around two dozen animal welfare charities have backed pleas to move the animals.
The Express was threatened with legal action earlier this year by the aquarium for daring to say its penguins were "captive".
Campaigners want Sea Life London, which is owned by Merlin Entertainments, to halt all penguin breeding programmes, permanently stop the exhibition of the animals and move them to a facility that provides a more naturalistic environment.
Gentoo penguins are native to sub-Antarctic islands where chilly temperatures allow for ideal breeding, foraging and nesting conditions.
Freedom for Animals described how the aquarium enclosure only allows them to dive to 7ft - a far cry from the 600ft in the wild.
A spokeswoman for Sea Life London Aquarium said: "The welfare of all the animals in our care is of paramount importance to us at Sea Life and we are committed to delivering the highest levels of care through our team of dedicated welfare experts, both internal and external.
"The gentoo penguin habitat at Sea Life London Aquarium was designed with help and advice from specialist vets. It provides an excellent balance of water and land for the penguins which enables them to express their normal behaviours and there is space for them to ensure they have sufficient privacy.
"As part of its overall mission, Sea Life London Aquarium has an opportunity and responsibility in sharing the wonders of the natural world in an accessible manner. With the opportunity to influence more than a million people who visit Sea Life London Aquarium from all around the globe each year to care for the world's oceans and the marine life within it, we believe this is a hugely positive thing."
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