Hello, I believe they will contact both referees, as they did in my case. I had one that was too long ago (from 2008-09) even though as a travel agent was more relevant I thought, so I had to provide them with another.
I have just had my Alcohol and other drugs test yesterday (AOD.) They tell you that you pass on the day which is fab. Now medical tomorrow. Seems pretty extensive judging by the forms. So many things they apparently check. Not looking forward to injections :-0