Most people won't apply for team leader. Basically, ask for an application form at the customer service desk (you don't need to hand in a cv). It has the usual - personal details, 2 references (I didn't have any, mind), the hours best for you, and a little quiz at the back of the form (as described above; what your good/bad at, useless in my opinion). Hand the form back in, they'll send a letter within the week saying they've 'recieved the application and are considering them all at the moment.'
At that point, don't count on anything. It took three months until I got a phone call asking me to come in for an interview. Completely forgot I applied there. Went to interview (wore smart trousers and a white shirt, but felt so overdressed). Mine was a one-on-one interview, they asked questions about teamwork (examples, etc), how you overcome failure, motivation, working with people you don't get along with, improving skills, communication, using your initiative. Basically everything tesco is not. What they really should have asked was "Can you follow instructions?" and "Can you put that box on that shelf?" You're not paid to use your brain in tesco. After interview was over, was told that I'd get a call back if I was sucessful, after that you start they get you to come in (paid) on a saturday to watch a few videos about tesco as a company and working there. Then answer a few questions on a sheet of paper, and listen to the people complaining at the "difficultly" of the questions and how there was "a lot to take in."
I could keep going into what it's like to work in tesco, but I'll leave it at that. You don't need to know anything about tesco as a company before your interview, but it might be a good idea to think of a few examples relating to "Teamwork", "Communication", "Helping people" and "Difficult situations". Otherwise you might find yourself waiting for a couple of minutes after the question is asked, trying to think up something to say.
Hope that helps someone, it's not difficult to get into tesco once you've got an interview though.