Beware of connecting to another destination through the UK on British Airways

This is a warning to everyone travelling on a South African passport. Do not fly British Air for any international destination except the UK. If you are connecting to another flight from a UK airport, even if you are there for a couple of hours and not leaving the airport or the terminal, you have to have a 'Transit Visa'. I booked a trip to Croatia using online bookings. While the site did say is to be sure to get visas, it did not specify that a UK transit visa is required when one is not leaving the airport.. I had never heard of a transit visa before. I have traveled, connecting through Germany, Italy, France, Hong Kong, Singapore and Abu Dhabi and have never required this. So I arrived at ORT airport to be told that I could not get onto the plane. I had to buy another ticket to get to my destination. And needless to say did not get a refund for the BA tickets.