Their post announcing the Pride and Prejudice documentary, mentioned earlier, cites a contactmusic article about Colin Firth's refusal or inability to participate, with the expected speculation about his Darcy-denial. There was also a follow-up post with more details about the documentary from Paul Fisher of KeiraWeb.com:
He spoke with the producer, Toby Stevens, who also produced the Comedy Connections documentary. The P&P documentary will follow a similar format, showing “the early careers of the cast and major crew (director/producer etc.) and how they came together for the production, what they’ve been up to since and lots of interviews and on-the-set footage,” Paul wrote. We can hear the fangirls swooning already.
Mr. Stevens did not mention a broadcast date, but Paul speculates that it will be shown in mid-September to correspond with the premiere of P&P3.