The Channel Islands are not part of the UK (they are Crown Dependencies) but, along with the Republic of Ireland and the Isle of Man, they are part of the Common Travel Area. There are no formal border checks within the CTA but whether you are flying or travelling by ferry you must have acceptable photographic ID. What type of ID is acceptable depends on the airline/ ferry company concerned. ID requirements for airlines which serve the Channel Islands and Gatwick: Loganair: https://www.loganair.co.uk/travel-help/id-requirements/ Aurigny: https://www.aurigny.com/faqs (Scroll down to the 'Photographic ID' section.) Easyjet: https://www.easyjet.com/en/help/boarding-and-flying/travel-documents-and-information If you don't have acceptable ID you won't be able to fly or take the ferry.