The following guidance has been issued by the HSE: HSE eBulletin: New webpages on driving and riding safely for work
You should ensure that you risk assess all your driving operations undertaken by workers and that the same is covered by your Health and Safety Policy to ensure that work is set up in such a manner that it does not result in excessive driving and allows workers to take breaks from driving. It can also be useful to provide overnight accommodation.
When you have completed your assessment, it can be helpful to remind employees of their obligations such as in the example letter.
If you find you need further assistance with assessing driver risks, we are able to offer: