I have here a shiny review copy of Russell T Davies/Benjamin Cook's updated version of The Writer's Tale (aka The Final Chapter). I'll be reviewing it next week, and then one of you lucky people can have it in a totally random competition.
But on p662, I found these exciting nuggets on information that should help clarify a few things in The End of Time that are causing controversy.
Euros has just been on the phone to Timothy Dalton, about playing the Lord President! TIMOTHY DALTON!!! AS RASSILON!!! Early days, of course – it's still not a definite booking – but it's as close as it can be. (I wanted the bloke from The Five Doctors, but apparently he was banned from acting ever again.)
Then, in a footnote, "In 1983 Doctor Who Special The Five Doctors, Rassilon was played by the late actor Richard Matthews."
So definitely the same Rassilon then.
Oh, and Claire Bloom is playing the Doctor's mum! (Yes, that's what she's been told, too.)
That looks reasonably definite to me.