Campaigners have demanded more transparency over the welfare of 15 penguins captive in a basement aquarium enclosure.
Sea Life, which operates the London Aquarium, has long been criticised by campaigners for its record on animal welfare and conservation.
The law requires it to provide data to local authorities about the animals in its care, including how many die each year.
But the aquarium has stopped giving copies of stocklists to the local authorities that license and inspect its aquariums.
Instead, Lambeth Council officers log into an online platform to see the records.
This means the Council said it had nothing to provide to requests for copies of the London Aquarium's records under freedom of information (FOI) laws.
When approached for the data, the council said: "We are not at liberty to disclose screenshots of the portal stocklist as, although we are granted access to the stocklists, we do not hold this information on file."
Dr Andrew Kelly, director of Freedom for Animals, said: "One of the biggest problems with aquariums is their lack of transparency and openness - there is no requirement for aquariums to publish their stock lists, the provenance of their stock, mortality rates or cause of death.
"They do however, have to provide local authorities that licence and inspect its aquariums with this information.
"Sea Life provides this information to local authorities via an online platform which is not accessible by the public and therefore avoids public scrutiny. If Sea Life and other aquariums have nothing to hide they would be happy to publish this data."
Lambeth Council last inspected the London Aquarium in September but has yet to publish the report because "the new licence has not yet been granted".
There is an informal inspection once every year while a "ull periodical inspection" takes place every six years.
Campaigners from Freedom for Animals will tomorrow at 1pm protest against the windowless basement penguin enclosure which lacks fresh air and natural light.
Liberal Democrat MP Danny Chambers said the time for Ministers to get involved in saving the Gentoo penguins is now.
He added: "The government must work with the local council to ensure the penguins are removed from this poor environment and given space to thrive. With the government already looking at updating the rules on animals living in zoos, now is the perfect time to act.
"The council also has a key role to play, by making public their report on animal welfare at the aquarium. They must now detail what so many of us have seen, which is 15 penguins deprived of sunlight and freedom.
"Every day of inaction is another day when the beloved Gentoo Penguins are forced to leave in completely unacceptable conditions. Enough is enough - it is time to free the Gentoo Penguins."
Sea Life London Aquarium has said the gentoo penguin habitat was designed with help and advice from specialist vets.
Lambeth Council has been contacted for comment.
Sea Life London Aquarium has been contacted for comment.
A Sea Life London Aquarium spokeswoman 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.
"Sea Life conforms to all requirements under the Standards of Modern Zoo Practice by providing the relevant zoo licensing authorities with access to its animal records.
"This is in addition to regular visits including zoo licence inspections by these local authorities, alongside additional external inspectors and independent vets, who monitor animal welfare and data on an ongoing basis and will continue to do so.
"Sea Life London Aquarium also carries out its own regular health checks on all the animals in its care, while an independent specialist vet also visits every two months for routine assessments, and can also be contacted daily with any other concerns.
"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 provides an opportunity to share the wonders of the natural world in an accessible manner. With the opportunity to educate 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."
You may also like
Alexis Mac Allister sends Liverpool title message before Brighton - 'Long year'
The Diplomat star Keri Russell's life from film debut to famous partner and 'anxiety'
Life-sized Taylor Swift cake created by baker but it's missing vital body parts
Arsenal drop new Gabriel return hint after Mikel Arteta's Newcastle admission
Man United have already blunted Enzo Maresca's secret Chelsea weapon ahead of Premier League game