Surely if checkin allows you to checkin then it should be with at least minimum adequate time to get through security to the gate before gate closing time? This obviously implies going straight to the gate with no shopping! After all the last thing the handling agents want is to be offloading bags.
On saying this personally I usually find the checkin and gate experiences as the lowest point of using Luton.
Recently passing through security most of the lanes (80%?) were shut.