The trust has now called for a boycott of Swedish goods until Oslo promises to deal more humanely with future cases.
Tony Banks, Labour MP for Newham North East, has put down a Commons motion on the subject which has been signed by 32 other parliamentary tortoise fanciers.
A European Union import ban on Mediterranean tortoises has raised retail prices to between pounds 90 and pounds 130. As a result, smuggling is common and there have been a number of cases of "tortoise rustling".
Although the Swedish consignment was of Russian Horsfield's tortoises, which can be imported, it was impounded at Arlanda airport in Stockholm because its importer did not have the correct paperwork.
The animals were kept in the airport for a week, during which time the Tortoise Trust, alerted through a tortoise-lovers' Internet site, tried to persuade the authorities to repatriate them. But at the end of October they were put into a refrigerated container which killed them within a few hours. Jill Martin, who runs the Tortoise Trust sanctuary in Wales, said: "We got the strong impression that there wasn't really any intention of doing anything other than destroying them."
The Swedish Charge d'Affaires in London, Marten Grunditz, said there was no rescue-centre in Sweden willing to take the animals, and they were not fit for transportation.