Qwertyplop
F3G failed, so I'll try. (Why? Dunno.)
The problem is not about immigration control, or how assiduously or otherwise the UK polices its borders.
It's about the places it is done in, and the management of the people who do it.
The places are awful, especially, but not only in BAA airports, which is not the fault of the UKBA. It is up to the airport to supply the place in which UKBA personnel work. It can supply a pleasant, cheerful, well-lit, spacious environment, capable of handling large variations in flow without seriously incoveniencing the airport's customers provided that UKBA does its job well and supplies sufficient staff when required.
Both parties have a clear role to play, and the problem is that in some airports and at some times the management of both is bad, as evidenced by the outcome of long queues in dreadful surroundings. That is what is so shaming; the UK looks and feels like an impoverished third-world failed State on those occasions. The controls themselves are neither here nor there.
For the airport, it is a long-term issue of better design, and a shorter-term issue of good planning of effective building maintenance. Forgetting about its shops would be a good start.
For the UKBA it is a matter of better staff management.
For both, it is a matter of pulling their fingers out.