The stowaways are believed to be from Vietnam, and were found by police in Surrey, southern England, yesterday.
Police photos showed the brand-new Italian sports cars on the back of a trailer, with clothes and shoes in the trunk of one of the vehicles.
"The nine adults were arrested and a juvenile was detained on suspicion of illegal entry into the country," a police spokesman said.
The spokesman declined to say where the trailer had come from.
The adults were transferred to the UK Visa and Immigration centre in Dover, a common entry point into Britain for stowaways on vehicles coming from France.
The news came as Prime Minister David Cameron on Thursday announced a draft law to tighten a crackdown on illegal immigrants.