If your clients want to cover a lot of the country in a short time, or just want more flexibility, they will need their own transport.
In order to drive in Scotland, non-UK citizens will need to supplement their national driving licence with an international driving permit, available from state and national motoring organizations at home for a small fee.
If they're bringing their own car into the UK they should also carry their vehicle registration or ownership document at all times. Furthermore, they must be adequately insured, so they need to check their existing policy.
Follow the links below for more information on driving in scotland, chaffeur service and car hire