Law is of no value unless it is enforced and breaches carry sanctions. Those who do not report breaches they are aware of act to undermine that law, albeit in a very limited way. This allows people to take advantage of the laxity in enforcement to obtain commercial advantage.
Throughout my legal training, I have been taught to model companies as doing what is cheapest (or what makes the most money) irrespective of the law. Clearly this is a worst case scenario, but some companies do break the rules knowing that the likelihood of getting caught is low and the likelihood of anything other than financial penalties levied on the company is even lower. The worst cases do lead to public inquiry action against the O licence and/or the repute of the Transport Manager, but relatively few cases reach that point.
Most offences have a component known as mens rea - the guilty mind. You can only be guilty of murder if you intended to kill or cause serious harm by your actions; absent that intent, the most you can be guilty of is manslaughter (which has its own mens rea component). Traffic offences are typically strict liability - they have no mens rea component, so you are guilty on the facts alone. There may be defences possible in some cases - if you moved into a box junction and stopped to let an emergency vehicle on blues and twos past it may be decided that you are not guilty - but these are mostly discretionary. There are few absolute defences in traffic law.
This leads on to discretion. Clearly the police and VOSA need an element of discretion - there may be circumstances in which the offence was completely understandable or it would be unjust to prosecute. A prosecution for being 1% overweight on a bulk tipper where the load had been rained on since loading would not be in the public interest and would be manifestly unjust (especially as the weighbridge tolerance may explain the apparent excess weight).
Unfortunately, the greater the degree of discretion allowed, the greater the possibility of arbitrary decisions. Why should West Mercia Police let Billy go when he was 15 minutes short of his required daily rest when Devon and Cornwall Police let Alice go when she’s 30 minutes short of her required daily rest. If it was that PC Angus Nairn (for the sake of argument - he is with West Mercia, isn’t he?) was having a good day and the weather was fine, but the Devon and Cornwall officer was short on her targets for prosecutions and it was raining, the decisions were surely arbitrary and unjust.
There is a strong argument for limiting discretion so far as that is possible, so that the law is applied uniformly.
More generally, why are there legal limits on road traffic? Though individual rules may not make a particularly effective contribution, the overall aim of the majority of traffic law is safety. Compared to many countries in the world we have relatively safe roads, where the majority of drivers are properly qualified and insured, drive adequately maintained and safe vehicles that are safely loaded, and are not excessively tired or medically unfit.
There is always pressure to run bent, especially when drivers are paid on a piece work basis and companies are concerned about meeting customer demands with the lowest possible spend on vehicles, drivers, maintenance and fuel. This pressure is only increased by other operators who run bent - the more companies that run bent, the less competitive an operation that follows the rules can be.
I come down very much on the side of the rule of law and due process. Those that break the rules should know that there will get their chance to put their case, but they should nevertheless expect penalties to be forthcoming. This levels the playing field for everyone and acts to improve safety. Enforcement should be targeted at the most likely offenders - if intelligence and inspection results show lorries from particular countries are more likely to run bent, they should be targeted. However, the same standards should be applied to all.
If people are running bent, why should drivers collude in the deception. Is it not better for the road haulage industry as a whole if the police, VOSA and CPS go after those deliberately breaking the rules and compromising safety to obtain commercial advantage? Lives could depend on it - a driver nodding off or finding himself with inadequate time to break due to excess speed typically has much greater consequences when the vehicle in question is a 44t artic rather than a 1.5t car.