MADBAZ:
I understand about the need for ADR but when or what quantities does ADR come into force. I can’t find any info on what the limits are, with the prospect of doing agency work shortly I don’t want to fall foul of this or any legislation.
Hi MADBAZ, There’s no need to worry on that score mate, because the UK’s dangerous goods Regs provide a statutory defence, if you can show that you were misled.
Let’s imagine that a “sender” tells you that the load isn’t subject to the Regs, so you take that info in good faith… then you set off…
Then the police/VOSA check you and find that all isn’t well… 
Then you get the caution “If you do not mention, when questioned, something that you later rely on”…etc.
That’s the time to say that Mr/Ms X told me it’s not an ADR regulated load.
All you need to do is to exercise “due diligence,” which IMHO would be to ask for something to be written on the documentation for the load.
There’s no point in you taking a fall for somebody else’s ignorance (or deliberate naughtyness.)
In any case when the sender is relying on an exemption, your load documentation should be endorsed (by the sender) with something like: “Load not exceeding the exemption limits prescribed in 1.1.3.6”, or maybe “Carriage in accordance with 1.1.4.2.1”. The owner of the vehicle also bears a legal responsibility in this area of the Regs, so it’s in their interests to communicate with the sender and ascertain what’s what before they allocate the job to a particular driver.
This makes sense, because the owner of the vehicle would know whether or not their driver is ADR qualified. 
Another point to bear in mind is that it’s not normally a driver’s job to decide whether / how much of the ADR Regs apply, even if that driver is ADR qualified.
Such training is outside the scope of the drivers’ ADR course.
To be properly qualified to make that kind of decision, you’d need another (very difficult) course called “DGSA” which usually costs the thick end of £1,000, plus you’d need a rather heavy set of law books to hump around with you. 
There are quite a number of exemptions to the Regs, so in some cases it’s perfectly legal to drive a truck full of dangerous goods without ADR applying to it.
Some commonly used exemptions:
- An exemption relating to the individual size of a package. (Limited Quantities)
- An exemption relating to the total amount loaded (When NOT carried in Limited Quantities)
- An exemption relating to the nature of the transport operation
- An exemption relating to a particular dangerous substance or article
- An exemption relating to a “Special Provision”
- A (road Regs) exemption related to the fact that the goods are considered dangerous by a different set of Regs, which apply to other modes of carriage, eg. trains, ships or planes.
- Any one of a vast number of other exemptions, which I keep in a secret cave.

i’ve dealt with some specific questions on exemptions in THE STICKY at the top of this H&S forum, which might be worth a read to familiarise yourself that the above concepts are OK.
MADBAZ:
I understand that you can only have 1600■■ litres of diesel on the truck, but what if your carrying 8x100 litre drums of patio cleaner (corrosive) for example, do you need ADR?
Sorry MADBAZ, I’m not sure where you got that info, but from a purely ADR point of view, it’s wrong.
The fuel exemption is for 1,500 litres as Coffeeholic said above.
Now it gets a bit tricky, because there are several sets of Regs at work at the same time. There’s Customs and taxation and Construction & Use and maybe some others too, so I’ll stick to ADR’s view of it.
1,500 litres of fuel may be carried in various tanks on the truck, whilst 500 litres of fuel may also be carried in a tank fitted to a trailer, plus 60 litres of fuel may be also be carried in jerricans. ADR goes on to say that other pertinent legal provisions must be complied with, so that’s where the other Regs might impact on what ADR says.
Sleep easy mate, cos most of this ain’t your problem. 