LGW Immigration for U.S. citizen

The one and only time that I flew into LGW from MCO we arrived at the South Terminal. I knew nothing at all about LGW, still don’t really, so I just followed the crowd to immigration. It seemed to me that I followed the crowd too far. When we walked down into the immigration hall I saw that non-British passengers were checked through on the left and we had to skirt around the larger group of British passengers to get there. At the same time I thought that I noticed a different entrance for the non-British passengers that we maybe should have taken instead of following the larger group. Is that the case? I hope I make myself clear.