In all cases staff can fiddle so all U can do is what is reasonable noting that staff who take drink and drugs like to hide the fact but this is an area that U have to consider and U also need to allow staff adequate time to drive from one place to another especially today [2015] where we generally have a risk adverse workforce In the case U describe staff bring in their insurance [which includes business use], MOT [where applicable] and driving licence on a regular basis for their manager to formally check and they make a declaration stating that the vehicle is well maintained according to manufacturers specifications - and managers undertake task talks about the subject and instruct staff in the appropriate policies etc. with adequate records kept of all these managing activities Business use [according to our insurers] should be included on the drivers insurance but this should not cost the driver any more money and to date this has been the case and defensive driving courses are not undertaken as we found them not to be useful Where Highways law applies RIDDOR does not apply, however RIDDOR does apply where Highways law does not apply e.g. whilst driving on private roads etc. such as in a college campus, private business land and HSWA etc. apply all the time as does common law To cover the company I advise that adequate records are always kept so as U have a defense as its funny how people forget what has been told to them etc. after they have had an accident You sound like that U have most things covered just a few tweaks are needed; best of luck