British people also avoid sharing tables whenever possible. However, when that isn't possible (because all the tables are occupied), the next best thing is to pick the table with the fewest other people on it (i.e. yours, because you're on your own) and politely ask permission to sit there. But not try to make conversation with strangers. That's just wrong. Clearly this person was a bit dotty.

The solution is either to go to less crowded places, or to bring someone else with you. Preferably someone who also has a lot of work to do, and who you don't particularly want to chat with.