Very easy to understand how it can take a while at Liverpool airport. Most times I have been held up there, they are staffing one x-ray machine and queue, whilst keeping the 2nd open for priority passengers who pay £3 or whatever it is to fast-track.
Nothing more than a case of under-staffing (either intentional or illness, holidays etc) really. Some cynical types would say that they are intentionally doing it to make the paid for option more attractive...