I think Sam you are living in dream world if you think you are going to get any service guarantee from anyone. As the UK Border Agency is a government institution I suggest you write to Dave and ask him what he is going to do about it. Some years ago I remember people complained about the lack of staff at UK Border posts and were told in no uncertain terms by members of staff write to Tony Blair or Gordon Brown!
Also I have used other London airports and have to queue to get through but for some reason Luton seems to be the worst unfortunately. As I said earlier ''Welcome to the UK''.