when i went through the whole long drawn out process, my referees were contacted by phone. They had to answer about 20 questions about your reliability, integrity ect ect. That being said if you get to the referee stage then there is a really strong chance you will get in. There has never been a better time than now to get into ATC - they want to rate some ridiculous number like 90 or so people this year apparently, so if you pass the testing day and dont make a fool of yourself at the interview then your chances are very very good.