I will be travelling to Vietnam on the 16th of December and spending one day in Ho Chi Minh City and another 7 days in Hanoi, which mean I won’t need a visa.
However after visiting Hanoi I have a flight booked for Phu Quoc Island and stay in Phu Quoc for 17 days. I’ve heard that British citizens get 30 days free visa. I was wondering if I will need a visa for Vietnam or not?
You should notice that UK citizens have 15 days visa exemption, not 30 days as you have heard (learn more about Vietnam visa for UK citizens)
Moreover, 30 days visa exemption for the travelers visiting Phu Quoc Island only applies if they go straight to Phu Quoc and leave without entering main land Vietnam (the travelers can transit via Ho Chi Minh City).
In this case, you will travel both Phu Quoc Island and Vietnam mainland and your entire stay exceeds 15 days that visa is required.
You can apply for 1 month single entry tourist visa at the cost of 15 USD (exclude the stamping fee 25 USD you will pay in cash at immigration counter at arrival airport) through www.visumvietnamonline.com.