I think I will give your post my 100% backing GTB!

In fact, the BRE document to which I referred to above, dated though it is, says;

"Workmanship

The objectives of building regulations and codes of practice and of building designers to achieve buildings which are fire resisting will be lost if good workmanship in the factory or on site is not achieved. 

Good quality control is important......but it becomes more important with those fire protecting materials which can be applied by unskilled labour. Education in the needs of quality control must start with the Architect on each new project..."

In that regard, it goes on to highlight the importance of the roles of the site engineer and the competence of the person applying the fire resisting measure.

Sadly, in my experience, many of the sites in todays building industry do not have the quality control that the document promulgated!

I think that there are two issues here:

(1) Workmanship. How can one put it politely? We have some tradesmen in at the moment and some of the work is a little disappointing. That said, if they took their time and did it better, the work would cost more. By contrast, I have every confidence in another tradesman who came to do some work for the first time today. At this stage, I will admit to having a streak of perfectionism, but not to a pathological standard!

(2) Contract compliance. Surely a building owner (or tenant even) would want to ensure that a contract is being performed. Perhaps, like yer average householder, they have no idea how to do that.

Personally I would opt to use a metal back box/KO Box  even in plasterboard/dot and dab.  Cut the whole and then use a metal dry lining bracket, then screw back box to it.  Several benefits

Metal is more robust

Plasterboard is not the main support for the electrical accessory.  (How many time the plug goes in and out that the socket becomes loose?)

Metal is less likely to catch fire than the plastic backbox.

Metal backbox will take longer time to melt than a plastic one.

Intumescent pad can be fitted behind or in from on the metal back box and any remaining small penatrations can just be sealled with something like FireMate (other brands are available)

In general I think there is a real lack of understanding by the trades about using fire seal on every and any penetration of a build fabric.