The rare Indian Star Tortoise (Geochelone elegans) is a species found in dry areas and scrub forest in India and Sri Lanka.
It is popular in the exotic pet trade.
The Indian Star Tortoises, worth more than 2,000, pounds were discovered by UK Border Agency officers in a parcel which had travelled by air freight from Thailand.
The breed is protected under international law and inquiries by officers revealed the necessary permits had not been obtained, the sources said.
Colin Brown, the UK Border Agency's assistant director at Manchester Airport, said: "The illicit trade in endangered animals is a serious contributory factor to the threat of extinction faced by many endangered species".
"Anyone tempted to trade in protected creatures and plants should think again, and companies need to make sure they have the right paperwork before they import exotic animals into the UK," he said.
Brown urged holiday makers "to ensure the souvenirs they buy do not contribute to this problem."
The sources added that the tortoises are being cared for in quarantine while plans are drawn up for them to be re-housed.
The intended recipient has been arrested in Manchester.