I cannot comment about easyJet. However, a friend of mine had this problem a few years ago with another UK company.
The Ops Director had a recruitment and retention problem. He sought to stem the flow by making it particularly difficult for the guy (an experienced Captain) to leave. Part of the bad practice involved was not actioning the request by the pilots next employer for a security reference. It did not, ultimately, prevent the issue of a pass or compromise employment. However, the pilot concerned suffered an awful lot of stress and angst as a result.
There are some decent employers out there. Unfortunately there are also some pretty bad hats who occasionally pop out from under their flat stones to play this kind of trick.
Obviously you are better off not working for such an employer - at least until they mend their ways.