The production team have now let the cat out of the bag, so we're free to tell you too: this year's Christmas special is the longest episode of Doctor Who since the series returned.
Here's what producer Phil Collinson had to say on the subject when we spoke to him a few weeks ago:
"I think it’s about an hour and ten now in total. It’s ten minutes longer than usual, which simply happened because we filmed a lot of material. We didn’t want to cut anything in the end, we edited it as tightly as we wanted to and still had ten minutes to play with, so that’s a great position to be in!”
The official Who site now confirms the running time as 71 minutes, which means that the episode will air at 6.50 on Christmas Day instead of 7.00, and that this episode is only beaten for length by 1983's feature-length 20th anniversary special "The Five Doctors". Or, come to think of it, that Paul McGann TV movie. But we usually try and forget about that...
Those of you interested in such things may like to note that Who is sandwiched between Christmas Day's two editions of EastEnders, and is pitted against an hour-long Emmerdale, followed by ten minutes of news.