A British man wanted on suspicion of murder has been arrested along with 17 suspected Albanian migrants at a South Coast marina.
The 55-year-old, who was being sought over a killing in Spain, was held with the Albanians at Chichester Marina in West Sussex.
Spanish authorities had issued a European Arrest Warrant for the Briton who is now in custody pending interview by immigration enforcement investigators.
He was detained on Tuesday morning on suspicion of facilitating illegal immigration, while the 17 Albanian men were held on suspicion of entering the UK illegally.
The Albanians have been detained pending Home Office consideration of their cases.
A Home Office spokesman said: "The security of our border is paramount.
"We work with our partners to detect and deter people who attempt to reach the UK illegally, while targeting the criminal gangs behind illegal entry attempts."
A locked facility with more than 1,000 berths, Chichester Marina is set in beautiful scenery and has a "marked air of peace and tranquillity", according to its website.
The discovery comes a month after the National Crime Agency (NCA) revealed that migrants trying to reach the UK are paying smuggling gangs up to £13,500 for their journey.
Some of those intent on coming to Britain are quoted five-figure sums to make the trip by air, while others are believed to have spent as much as £12,000 to travel from France in inflatable boats.
Investigators suspect that, as well as the main Channel crossing between Calais and Dover, criminals may be using less busy ports in the UK, including Tilbury, Purfleet, Hull, Immingham and Newhaven.
The desperation of some migrants to reach Britain was highlighted last month when two Iranian men were found floating in an ill-equipped dinghy in the English Channel.
A light on their mobile phone alerted a passing ship in the Dover Strait - one of the busiest shipping lanes in the world - before they were picked up.