Was in Premium Economy from LHR-SFO yesterday. A passenger next to me asked for a coffee with a small cup of milk on the side (I presume so she could regulate the amount of milk in her coffee). The FA said that it was not allowed. Is this actually UA policy? If there is a policy that passengers cannot drink milk as a beverage option, why not simply give the passenger the same amount of milk in a cup that would be allowed under the approved milk allocation per coffee. We gave each other a look and laughed as the FA was out of sight and went to the next rows.