Under China's 240-hour visa-free transit policy, British citizens can enter via Shenzhen Bao'an Airport or Shekou Port with a valid passport, confirmed connecting flight tickets to a third country (e.g., Hong Kong to Vietnam), and an entry card. Your itinerary meets the "transit" requirements, and Shenzhen is within the applicable regions. Notes: ① Must enter through the above designated ports (land ports not applicable); ② Must depart within 10 days starting from the day after entry (e.g., if entering on Day 1, must exit by 23:59 on Day 10 via any designated port). Confirm connecting flight times in advance and declare actively at the port.