If your hand is inside the pocket and you catch the cue ball, I'm pretty sure that many referees, strictly adhering to the rules, would call it as unsportsmanlike conduct -- with the penalty (which might be nothing more than a warning upon the first occurrence) up to the referee. You just don't want hands in pockets in top-level events. Haven't you ever seen a ball hit the back of the pocket and pop out? In lower-level play, just don't do it yourself. And if you don't want your opponent doing it, politely ask him not to.
Again, you keep mentioning the BCA rule book you have (from 9 years ago). It is obsolete. The 3-foul rule you mentioned, for example, has also been changed. See paragraph 4.11 Serious Fouls in the current rules. And are you aware of the stalemate rule? That was a significant change, too.