You dont need to have Law work experience. Its an academic course, and so it really isnt needed.
You just need to be able to show that you have a genuine interest in studying Law for 3 years - and why.
You could use a legal issue you are interested in, or a recent case, or some reading you have done, to explore this.
Many people who want to pursue Law as a career do get some work experience so that they have seen what the job involves - but even then it really isnt essential.
Most Unis dont interview anymore - exceptions are Oxbridge, or where you are a mature student etc.