Dick Van Dyke

When the Ninth Doctor tried to mimic Jackie Tyler, Rose told him "Dick Van Dyke wants his accent back." (COMIC: Weapons of Past Destruction)

When the Tenth Doctor mockingly said that he was convinced by "the whole posh, gravelly thing" present in the War Doctor's voice, the Eleventh Doctor said to his predecessor, "Brave words, Dick Van Dyke", implying that the younger Doctor had no cause to comment upon the authenticity of someone's voice. (TV: The Day of the Doctor)

Behind the scenes
The reference comes from the fact that Dick Van Dyke, an American, is roundly ridiculed in the United Kingdom for his poor Cockney accent in the film Mary Poppins. The joke also works on a meta-textual level since David Tennant played the Tenth Doctor with (which sounds similar to Cockney) instead of his natural Scottish accent.