Dick Van Dyke
From Tardis Wiki, the free Doctor Who reference
When the Tenth Doctor 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 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 Estuary English (which sounds similar to Cockney) instead of his natural Scottish accent.
