For the Company:
Copy of Certificate of Incorporation - then cross check this with Companies House.
Copy of VAT registration certificate if they are VAT registered.
For the owners of the company:
All Directors owning greater than 25% share capital of the company:
Name, Address, Passport Copy (you need to see original as well), copy of drivers license, a Document that shows their current address such as recent bank statement and/or Utility bill. These three should suffice.
If no one has more the 25% I tend to do at least 2 key directors (normally MD and Sec.).
That should give you most of the info to complete the MLR checks, document wise.
Hope this helps.