BBC Interactive editor Iain Tweedale told DS that BBC Worldwide will release the episodes monthly through "third-party game sites" for a small fee.
It was also explained that the downloadable series was to be released later due to scheduling differences of the show.
"It was always intended to be a bit later. So in the US the series is running a few weeks behind the UK, so that kind of fits nicely.
"But there are some key events happening in the US that we will probably launch it around, big gaming events, and so that's sort of the thinking there. But we obviously wanted to have it as close as we could between the two."
The second episode, Blood Of The Cybermen, will be available to download for free in the UK from Saturday.
> Click here to read our preview of Blood Of The Cybermen