British nationals will need a visa to enter Turkey, unless you’re a cruise ship passenger visiting a sea port or nearby city and staying for less than 72 hours.
You can obtain an e-Visa online before you travel through the dedicated Republic of Turkey e-Visa website. The e-Visa costs US$20, and can be applied for up to three months in advance of travelling. Be wary of unauthorised websites issuing fake e-Visas and be sure to get yours from the official channel. You’re advised to carry a hardcopy of your e-Visa with you in case there is a problem with the computer systems at the Turkish port of entry.
As of July 2017, it’s still possible to obtain a multiple entry visitor visa on arrival. These are valid for 90 days and cost £20, which must be paid in cash. However, this scheme is likely to end in the near future, so be prepared and get your e-Visa in advance to avoid any problems once you arrive.