Five suspected illegal immigrants were discovered hidden in the back of a lorry.
The shocked German driver parked his vehicle on the forecourt of the Guestling Garage in Hastings and called for help at 2pm on Saturday.
Garage assistant Wayne Novis said: "He came running into the garage and seemed quite shocked. We thought there was a fire in his lorry or something.
"He said he had noticed people hanging out of the back of the 40ft vehicle. He thought the people inside were illegal immigrants so we called the police immediately."
Officers arrived at the garage in Winchelsea Road and, with the driver, searched the lorry, which was covered in blue sheeting.
Inside they found five men - three Iraqi Kurds, one Afghan and one Arab.
A Sussex Police spokesman said: "Five men, who we think may be illegal immigrants, were detained for their status to be checked and taken to Hastings police station. They did not require any medical attention.
"The police will contact the immigration service and the five men will receive an interpreter if they need one. What happens to them next will depend on their country of origin and where they entered the country."
The lorry driver went to the police station on a voluntary basis to give a statement. He was asked to detail the route he took and where he stopped along the way.
The incident comes just days after Eurotunnel appointed General Sir Roger Wheeler to improve security on the cross-channel route.
The company wants to stem the tide of would-be immigrants who often risk their lives to get to the UK.
Eurotunnel blames the proximity of the Sangatte refugee camp in France for nightly attempts by large groups of asylum seekers to reach Britain via the tunnel.
The camp is only half a mile from the Channel Tunnel entrance and a mile from Calais.
It holds up to 700 refugees, mostly Kurds from Iraq and Afghanistan.
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