Not sure I can post link because it's from the Manage My Bookings link on the rentalcars.com web site ... I'm reluctant to post personal data on line.
But here is the relevant paragraph:
"Identification
Three forms of identification are required and can be: bank statement, utility bill, credit card statement, or other official letter stating home address, posted to the customer's current address within the last 3 months."
Then, on the rental agreement itself ....
"Identification
Two additional forms of ID are required to confirm home address, one of which must be a statement for the card being used for the deposit at the car hire counter. The other should be a formal document (utility bill, council tax bill, etc). These must be dated within the last 2 months.
A Passport is required."