Stephen Fry's Doctor Who episode moved to season 3

Last weeks film reviews with Mark Kermode (on BBC Radio Five Live and available as a podcast), included an interview with Mark Gatiss who mentioned that the Doctor Who episode that Stephen Fry has written is going to be moved to season three because it is too expensive to make this season. He also talked about writing an episode for season two that would live up to the scariness of "The Unquiet Dead", his season one episode (which included zombies at 7pm on BBC 1!). He reckons he has done it though.