London have several professional football teams. If you are visiting in a weekend you'll have plenty of options. For some (relatively) cheap and authentic football action, watch the teams from the lower leagues. But remember, there are also plenty of football opportunities outside London. Why don't you try to jump on a train, or perhaps one of the cheap flights to Leeds to experience tense football and a little bit of Yorkshire pudding? Or how about a trip to Birmingham to watch WBA, Aston Villa or Birmingham City?