What is the immigration process for transiting through Bangkok on a flight from London to Phuket?

When transiting through Bangkok to Phuket on a Thai Airways flight, if your tickets are booked on one itinerary, you typically won't need to go through immigration in Bangkok. Instead, you'll head directly to the transfer area for your connecting flight to Phuket. If your baggage is checked through to Phuket from London, it will be waiting for you upon arrival in Phuket. However, if you booked separately, you may need to collect your bags and go through immigration at Bangkok before proceeding to your domestic flight.