The Curtis Brown Literary and Talent Agency have cited a credit for Doctor Who on their profile of director Peter Hoar; the entry reports that he will be directing a "one-off Special of the popular series to be broadcast over the Easter weekend", a one hour long story written by Steven Moffat and produced by Marcus Wilson.
There is no other confirmation on the details listed; filming for the new series during November saw the completion of the opening story penned by Steven Moffat, and then moved onto Matthew Graham's two-part story (as reported by the writer), so the production date given remains unclear at present.
The positioning of such a special within the series is also uncertain - though Doctor Who traditionally broadcasts from around Easter, 2011 sees the weekend fall later in April (22nd-25th); this might suggest that an earlier Spring start to Series Six, but previous years have shown that any such decision is unlikely to be confirmed until a few weeks before transmission.
Update: since the news item was published, the profile listing has now been adjusted to read "Director of a single episode to be broadcast in 2011".
Hoar's CV includes the BBC's popular spy series Spooks, Mistresses, and ITV's crime drama Wire in the Blood.