I too was curious about the LAW on this…
FROM THIS DISCUSSION
Coddy:
I too want to know exactly what the law says on this, a lecture I went too on digi tachs, the guy said it was an offence if the truck is set at 56, to go over that for more than eg 10 seconds, as this showed up overspeed on the memory, and was now and OSL (Overspeed on Speedlimter offence) despite the law in the UK still being 60 mph for trucks on the M/ways.
Is there a specific law on going over the limiter if it is still under 60mph on a UK motorway 
My understanding of the law is that as the vehicle is by law limited to a maximum of 56 mph (89 kmph) it’s an offence for the vehicle to be powered at more than 89 kmph, but it’s certainly no offence for the vehicle to be driven at 60 mph as long as it’s not the engine that’s forcing the vehicle to go at a speed that exceeds the limiter speed, rolling downhill for instance.
So the answer to your question is that there’s no law against going over the limiter as long as you’re not breaking the speed limit.
There’s nothing to stop companies from having their own in-house rules on it though 
tachograph:
There’s nothing to stop companies from having their own in-house rules on it though
so Company policy not LAW then
ROG:
tachograph:
There’s nothing to stop companies from having their own in-house rules on it though
so Company policy not LAW then
Absolutely, but exceeding the limits set by the company could lead to disciplinary action being taken against the driver.