After this week's dreadful events, you would have thought that Luton's security staff would have been on the ball.
Warning, a politically incorrect view now follows: I might have expected them to be but there was no need.
After the great success of 9/11, the low tech approach (Madrid) has worked very well for them. Also, a photograph of Luton Airport has no value to these people. They want the 'postcard' targets, which is why central London got done. Whilst LHR might be a target, LTN is much safer.
Of course, there may be some wild cards who will try their luck but, I doubt it. If they wanted an airport other than LHR? Gatwick is well known internationally but they would probably want an airport that is closer to a city that is understood by people in the middle of the desert.
I have said since 9/11 that flying continues to be the safest way to travel - for many reasons.