They were bringing furniture back from a house they'd sold in France.
"We had just unloaded part of the trailer, and I was looking to see what to do next," Sue told BBC Wiltshire.
"Suddenly, two immigrants appeared, which is a really horrible fright when it first happens."
"Then there were two more in the back of the trailer hiding under bin liners," she said.
"They looked absolutely exhausted and they were just standing there with their heads down."
They said they had placed tamper proof tape and fastenings. But they noticed they had been damaged after returning from dinner in Caen before boarding the ferry, and raised their concerns with border officials.
"They climbed up and looked in but couldn't see anything untoward," said Jeremy.
Three of the four arrested are minors, now in the care of Wiltshire Social Services. The fourth has been transferred to an immigration removal centre where his case will be handled.