Right, being a huge Doctor Who and 999 fan, I couldn't help but flail violently at how similar this episode was to the game. SPOILERS AHOY!
The episodes name is "The God Complex", and it's the eleventh episode of the sixth series.
The basic plot is that "The Doctor" and his companions find themselves trapped in what seems to be a 1980's hotel with constantly changing corridors. There are four other people who appear in the hotel with no idea how they got there.
The location itself was quite similar to 999. All of the windows and exits were boarded up or sealed shut, there are numbered doors (however, in this, they represent the characters fears), there's a room that looks almost exactly like the bar/lounge in 999, and here's the big one: It winds up being a simulation!
You should give it a watch, I personally like the episode because it reminds me of 999, but that's just my opinion.