Most prosecutions proceed on the basis of police giving evidence about the alleged defect or other contravention, such as driving with an insecure load or too many passengers. In a large number of cases the evidence will be relatively straightforward and the defect or danger will be obvious. In other cases, however, the police evidence will be highly subjective and open to question. It should not be assumed that the police have the necessary expertise to give evidence about technical defects and the inherent dangers. Nor should it be assumed that the evidence of the police cannot be challenged. A factual defence of denial is always open to a driver who disputes the allegation that his vehicle does not meet the required standard.
Nonetheless, it is important to note that ignorance of a regulation or a defect is not a defence. These offences can arise even where the driver was unaware of the defect. Therefore, if a driver is charged with using a vehicle with defective lights it is not a defence that he did not know that the lights were not working. A driver is expected to check all is in order with a vehicle before setting off.
If a driver is convicted or accepts that he is guilty of a Construction & Use offence he may avoid penalty points and disqualification if he can show that he did not know, nor had he reasonable cause to suspect, that the offence in question was being committed. The onus is on the defence to establish this requirement on the balance of probabilities.