If it helps, Airservices called me a few days before they contacted my referees to let me know they were going to. Not sure if this is standard practice, but I thought that was very nice.
In any case it didn't matter too much as I had tried to take the assessment day off as annual leave and my boss said "No, I need you here that day". I then had to tell him it was for a job. He hadn't realised I was looking so was a bit shocked, but at least when it came round to me telling him he'd get a call in the next week for a reference, he knew what it was for
