Lucy:
dieseldave - My comments on the legality of pay schemes were separate from those to Steve, and are a favourite soapbox of mine as a majority mileage-paid employed driver. 
In practice, the interpretation of this particular piece of law varies from Traffic Area to Traffic Area.
All soapboxes gladly welcomed! And it’s true that the various TCs interpret differently. Most TCs have a legal background in transport law- they even have a quasi-judicial role. My point was that there’s an appeal procedure. When faced with a particular question, the TC will rule- that’s the way of it. However, one of the parties has a limited right of appeal, so the question might go via that route for a court ruling.
Lucy:
I now work for a firm an hour or so up the road and over the border between Traffic Areas and we are paid 28ppm basic and 30ppm after 1750 miles, plus various bonuses for reloads, multidrop jobs etc. and percentage of what the lorry earns. There’s also a local “job rate”. On paper we are contracted to 40 hours for approximately £250 on top, but that is purely on paper. In practice the vast majority of our very healthy (for Teesside) wages come from the mileage. The local Traffic Commissioner is well aware of this as the firm have been paying that way for 25-plus years, and keep a very close eye on us from a legal point of view, but otherwise all is deemed to be fine. (None of us want hourly pay, btw, we like working shorter hours for more cash).
Everything is fine as long as 561/2006 isn’t infringed. My point was that, if there were some big accident with serious injuries, and it got looked into in depth, then the idea of paying an employed driver a % of earnings might be questionable.
Lucy:
dave - It’s precisely because the loads won’t always be there that I’m suggesting the scheme that I am. The day rate/salary would have to be fair for the average hours on it’s own, the load bonus would be precisely that, a bonus, to give the driver an incentive to do the extra bit when it’s busy. 
I actually agree with you on this point, but I’d give the “bonus” a different name. I’m not encouraging anybody to break the law, but this idea can be made to fit the original question.
Lucy:
I don’t know…I guess because I’ve driven for the majority of my career on some kind of tip/mileage/percentage based scheme, it’s what I’m used to therefore I prefer it. I never liked hourly rate because of the length of the wretched hours needed to make the best money. To put it simply, I prefer to be paid for what I do rather than what I don’t do, if that makes sense.
Yes, Lucy it makes perfect sense. I was on trip money without bonuses when I started doing Europe in the early 80’s. That was so unjust, because we had to do our own repairs and change wheels on our own. Our boss even gave us spare inner tubes We didn’t get a penny more whether the trip took a week or a fortnight. Each trip had its own “rate.” In the late 90’s, I was on tanker work. Paid by the load with no allowance for tipping and loading. Tip/load was 1.25 hrs each. Do three loads a day, who was the idiot? (Rhetorical question!!) Thank God that those days are over.
It’s only fair that a driver is properly paid, without relying on loads of overtime to make a living wage. I do suggest that firms carefully consider the label that they put on the “bonus” scheme, because of the pitfalls. I strongly support your soapbox, mine is maybe a little higher and has the latest in megaphones I only suggest, with good reason, that everybody use caution.
We can make of it what we will, and so will the lawyers, but remember that the only place ultimately qualified to interpret law is a court 
(Yes, before anybody else thinks of it; a Traffic Commisioner may well have ruled on such a matter. However, there is an appeal process, so that’s the reason for the word “ultimately.”