Barry Letts (in-universe)

After Terrance Dicks mused that "who's for a brew" would make a good title for something, he said that he would "write it down and show it to Barry". (WC: U.N.I.T. On Call)

Behind the scenes
While it was clear U.N.I.T. On Call was referring to Barry Letts, only his first name was used.

In the real world, Barry Letts was involved with both Doctor Who and The Avengers, both of which exist in the DWU.