Well you posted this yesterday and the summer is already over, so I assume you are asking about next summer? If so, search out professors in the UK whose research you like and shoot them an email. Better yet, google study abroad programs, and ask your study abroad office at your college or university. There are programs like the DAAD RISE which sends Canadian and US students to Germany, and I'm sure there are programs that send them to the UK as well. A professor you randomly email might not accept you only because he would have to support you out of personal funds, whereas most exchange programs give the professor money to pay for your stay. That is not to say they won't accept you though, who knows. Best bet is google, or asking around your campus, or your professors