Staff at Bodrum airport confronted Toby Robyns, 52, after they found 13 coins in his luggage, The Sun reported Tuesday.
He is being detained in Milas prison on suspicion of “finding Turkish artefacts without notifying authorities,” according to The Times.
If found guilty, he could face a three-year jail term.
Robyns found the coins in Turgutreis, an area close to Yassi Ada island which is thought to be surrounded by up to 25 shipwrecks.
James Stoneham, a family friend, told The Sun: “This was harmless fun on a holiday. When he went to get his flight home they dragged him off and searched his hand luggage.”
Meanwhile, The Times reported that a Foreign Office spokesman said: “We are assisting a British man following his arrest in Bodrum and remain in contact with his family and the Turkish authorities.”