UK visitors arriving in Turkey should get an e-visa online before travel.

Obtaining an e-visa is the cheapest option and visas on arrival are due to be phased out which may happen without much prior notice.

Cruise ship passengers with ‘British Citizen’ passports entering the country for a day trip, remaining in the port of embarkation and returning to the ship the same day will continue to be able to enter Turkey without a visa or an e-visa.

For more information visit the Republic of Turkey's Electronic Visa Application System.

Source: http://abta.com/news-and-views/news/turkey-e-visa-reminder