The views expressed in this post are my own personal (HRA protected) views, and are not representative of any organisation I have any involvement with.
If you are not going to meet the client in person you need to carry out an online search instead of getting a photocopy of driving licences etc. There are quite a few companies that offer online identification checks for money laundering purposes. Most of them can access databases that provide both positive and negative information. Positive information can confirm an individual's full name, current address and date of birth. Negative information confirms that an individual is not on a list, such as that of deceased persons.
A search normally costs between £3 and £10. To satisfy the ML requirements make sure you print out the report and keep it in your clients permanent file. As long as the report is positive no further evidence is required.
HMRC love due diligence and in their eyes you can never do enough! If you are not going to meet your clients, see their offices, meet them in person, meet their staff etc, this would be seen as not doing enough due diligence. The list is endless but you must satisfy yourself that they are ok.
