The logical thing to do would be to firm either Southampton or Birmingham and then keep either Loughborough or QMUL as a backup. But you've got loads of time yet so don't rush into anything. Try and visit all of your choices, speak to students, look at all the modules, and only make a choice when you've looked at the pros and cons of all of them. Speak to people who know you, family and teachers. Listen to their advise but ultimately it's you that has to decide. Uni is minimum 3 years, so you have to be happy with your choice. I can't believe the number of threads on TSR that I've read lately with students dropping out mostly because they've chosen the wrong course or the wrong town, and sometimes because they've built up the idea that going to Uni is going to be an amazing experience every day, when in reality it's hard work.
So basically don't rush into it. Look in detail at the course, but also at the social side, the cost etc if it's an issue, and only make your choice when you've done this. There will be less chance that you'll be disappointed!