Quite so!Well when you knock out the knockouts on the back of a board, you open up a huge hole, we're talking the equivelant of 3 or 4 20mm knockouts. Most of the time this is mostly backed by plasterboard and isn't as much of an issue. When you then cut out the plasterboard to the same size (or bigger) to bring you cables through) there is now a huge exit for flames to shoot out of, up and into your stud wall.
The LFB really ought to understand this, and have incorprated it into their advice/demands regarding BS7671. I'm sure no-one would be happy with 'fire doors/barriers' that were required to be made of 'non-combustible materials' but which were allowed to have big holes in them Whatever BS7671 may have decided to write (and not write) about this, IMO containment is always going to be at least as important as 'combustibility' in these sort of situations.
Kind Regards, John