Even with electronic data collecting technology, no border, not even a sea ferry port, can be 100% full proof.
Under the last Labour government, UKBA were having their resources cut back, with experience staff being made redundant, and less experience staff filling their positions.
I once remember on a Dover bound ferry, being chatted up by an Irish speaking male. “Did I want to buy some cigarettes”, “No” I replied, “Watch customs pull me when we drive off” he informed me.
Sure enough Customs pulled his van in for a search, and also my vehicle. Three officers went through his transit van with a fine toothbrush, with one officer asking me a few questions, then allowing me on my way.
Later, as I drove up the hill away from Dover, the same white transit van, was being loaded with contraband from two parked cars.
Without the resources to pull, stop, search and question every traveler, then the UK will never have secure borders.