K.Adams:
Just a quick one.
ADR Do i require to have a lockable steel storage box on my vehicle by Law for the spill kit?
HI mate, the easy answer to this is “NO.”
K.Adams:
When I took my ADR I never heard of it, it was only my DGSA (he only just passed it) wanted me to have it on my vehicle.
Ahhh. The exuberence of a shiny new ticket… 
K.Adams:
I have everything ADR asks me to carry. so is it true?
ADR demands that you carry various equipment, but the exact list depends upon the substance(s) to be carried.
As an example, you’ll need to carry the following equipment once you have exceeded the threshold limit for the substance in question:
A. A wheel chock
B. Two self-standing warning signs (which can be cones OR triangles OR flashing amber lights.)
C. A hi-viz vest or warning clothing (to Standard EN471) for each person on board the vehicle
D. A pocket lamp for each person on board the vehicle
Additionally: A respiratory protective device (if required by ADR chapter 3.2) AND any other special equipment as required by consulting your Instructions In Writing (Tremcard) for the substance(s) to be carried.
So how do we know this?
The requirement is set out in the UK Regs [CDG 2007 Reg. 63(5)(a) and (b)] and ADR 8.1.5
Above, I’ve set out the requirements and provided the legal quote to back-up my assertion, so now I’d say it’s all very well this guy saying that you need a lockable steel box to be carried IN the truck, but he’s going to struggle to come up with a legal quote that says that you must carry one in the way that he suggests.
Speaking as a DGSA, I should explain that the way that DGSAs work now says that I must wait for him to show the legal source for what he says, OR simply wait for him to own-up that he’s got it wrong.
Speaking as an ADR instructor, I agree with you that the idea of a lockable steel box for this purpose isn’t mentioned in the ADR course. 
If you really don’t want to have to carry this box, please ask him to give you a quote that says you must, then post it on here and I’ll have a look.
It would be very unhealthy for us to hold our breath whilst we wait for him to provide a proper legal quote. 
K.Adams:
The box he tried to give me is one of those van safe boxes well its just sat in the yard now
IMHO, that’s a good move mate. 
To be fair to this guy, I can see that his intent was to get all your kit into one place where it would be free from damage / theft, but there are far better ways of achieving this as suggested, and shown by the pics put up by others contributing to this post. 
Everybody who’s posted so far has pointed out that the equipment “must be accessible” ---- but now for the strange part…
It’s not actually a requirement for the equipment to be accessible, but it IS a requirement for the fire-extinguishers. (ADR 2007 8.1.4.5) 
Clearly, many firms have adopted a commonsense approach to this and made the equipment accessible and placed it in external boxes, which is OK.
Equally, carrying the equipment (but NOT the larger of the fire-extinguishers) in the cab is also OK.
The smaller (2kg) fire-extinguisher CAN be in the cab, but must still be accessible.
From your original post, I’ve no way of knowing whether your DGSA had intended you to carry both your fire-extinguishers in the metal box as in your pic, which would be illegal, so it wouldn’t be fair of me to point a finger at him for that at this stage.