"It gets flung in and approximately zero care gets taken in terms of mechanical protection and adequate support"

That must not be allowed to happen in any installation, domestic or commercial.

Due diligence is required in either.

Cables and protection must be afforded in all installations none the less. Different likely use in some locations might need to be considered as to what may or may not be appropriate but that does not give us any blanket statements

Any reason you're not using singles?

If cables are going to be flung about above grid ceilings I'd prefer they were sheathed T&E rather than unsheathed singles! (not merely a rhetorical point, I have actually seen unsheathed singled go up a partition wall in conduit and then run unenclosed (other than the ceiling itself) over the tiles).

   - Andy.

We are using T&E because it'll be a cheaper and faster installation. It's not impossible to install the cables neatly as far as possible. Thanks for your opinion.

T/E is one of the best cables around in terms of optimum choice. Properly installed it will give service for many decades. Back in the 80’s as a contractor, we installed miles of the stuff, mostly in premises related to the hospitality sector but also in offices and shops that were blasted during the troubles in NI. Now 40 years later I have returned as an inspector and find the cables almost as good as the day they were installed! 
I thought then that that it was silly to look down ones nose at a perfectly sound wiring system. Now I know that it definitely is!

In relation to the OP, 4D2A was there long before 4D5. 

In relation to the OP, 4D2A was there long before 4D5.

Indeed. Historically we used what's now 4D2 for T&E (as well as circular section multicore cables) but then as more thermal insulation began to be used in homes, problem arose. Partly it was realised that the allowance for thermal insulation in the regs wasn't entirely adequate, but also that the shape of T&E makes it not quite so bad as circular cables (larger surface area, less thermal insulation effect from the thinner sheath). This article from the IET (IEE as it was then) describes some of the background: electrical.theiet.org/.../establishing-current-ratings-for-cables-in-thermal-insulation.pdf In that context it's perhaps not surprising that table 4D5 concentrates on thermal insulation related installation methods. 4D2 remains the 'fallback' for anything 4D5 doesn't cover.

   - Andy.

This question is horrifying. We should NOT provide design advice in this context. I was recently told by a proper designer that he was being asked to do some of the designers primary tasks on a "design" from a well know "consultancy" because they didn't know how! This is the state of the Industry - truly shocking, The answer to this question is clearly "Ask the Chartered Electrical Engineer who is in charge of the design process".

This question is horrifying.

I disagree - we all have to start somewhere and if you don't ever push yourself beyond what you already know and are comfortable with you'll never progress. Asking questions is always good - there will always be some holes in anyone's knowledge and far better to recognise that and seek answers than plough on in ignorance.

My advise is always make sure that the answers you're given make sense to your - never just accept things that don't seem to add up just on trust - and certainly never on the sole basis that whoever gave you the answer holds some piece of paper that says they should know what they're talking about. Pieces of paper are often wrong (the state of the industry when it comes to EICRs illustrates that) and even when someone does actually understand the subject properly it still doesn't guarantee they're actually understood your particular question correctly.

   - Andy.

Indeed AJ. I wonder where chartered electrical engineers go when they seek assistance, or perhaps they don’t need to if they know it all. For those that don’t, I would have thought that this forum would be a welcoming and understanding place to lay their chest bare!

There can't be that many Chartered Electrical Engineers left now, as the IEE stopped giving them out years ago.