According to his Twitter account, Dean Gaffney (ex-Eastenders) has been filming for Doctor Who, so it can only mean he is in the episode currently being made.
We did understand the Christmas double episode was next up for filming, but it appears they are back filming in order with 4:16 (a currently untitled episode, which follows the Easter special, Planet of the Dead).David Tennant, and his stunt double, have already been seen on set (Photograph by Scooty here), and he is back in the orange spacesuit first seen in the impossible planet!The section they are filming is rumoured to be set on Mars, and we all know who comes from Mars dont we? (for those that don't, its the Ice Warriors :) )
It has been further rumoured to also feature The Master in an identical Orange Spacesuit, please remember this entire last paragraph is made entirely from rumours, so please treat them as such!
Additional: People are suggesting the Twitter account isn't of the real Dean Gaffney, so the whole thing may be fake. We'll see anyway