Picture the scene...
A small group of very smartly dressed, tall and well-spoken people loitering around the corner of a suburban street after dark. The signal is given. They jump over fences and into a garden, inspect the briefs on the washing lines, snatch one pair and disappear into the night.
Later on, at a lab back at HQ, the briefs are analysed, and a report is tendered to N (the head of GCHQ).
"Fine work, men, and you too, women" says N. "Now we know what brand of washing powder they use, which was our first objective. However, our next step has to be to get a pair of unwashed briefs. This will give us clues as to their personal hygiene and where they shop for their underwear. Any suggestions on how we might go about it?"
"We could arrange for a burglary of the premises while everyone is out, and take a pair of briefs out of the washing basket" suggests agent 003.
"Too risky" says M. "What if they've just done the washing? There won't be any briefs in the basket. No, we need something which is less likely to end up in failure."
"How about using one of our Page 4 (TM) girls to lure them away to a sleazy hotel, and while they are having sex, one of our team sneaks into the room and removes the suspect's briefs from the floor."
"What if the briefs are not on the floor though?" asks N. "What if the suspect merely dropped them rather than taking them off altogether? It won't do. Besides what about the women and children? You are not suggesting that we deal with them in the same way are you? We need something more creative.
"How about an evening-time burglary while the family is having dinner" suggests 0021234. "We go in with a full swat team, including a Page 4 (TM) girl. We get the Page 4 (TM) girl and two of our special forces operatives to drag away the father to a sleazy hotel, with strict instructions that he's not to come out of that hotel with his underpants on. The rest of the family we arrest on charges of committing offences likely to foster terrorism: parking on a yellow line in the case of the mother, and being rude to teacher / not doing one's homework in the case of the children. We take them to court right away. They'll have to file their briefs. We switch them there and then, sight unseen, for other briefs that we will have just brought with us. Job done"
"Excellent" says N, patting the brilliant young recruit on the head. "Well done. Let's do it. I'm putting you in charge of this operation!"