When 'EastEnders' showed up on the TV screen in the "Army of Ghosts" episode of 'Doctor Who', I wasn't too concerned. After all, for the time being we're watching an alternate TV dimension's Doctor, not the one from the main Toobworld. (Although the general storyline remains similar between the two versions.) So in that dimension, 'EastEnders' is just a TV show, which means the RTD version of 'Doctor Who' shares the same TV dimension as 'Hot Metal', 'Extras', and 'Gimme Gimme Gimme'.
I realize it wasn't very good, but "Children In Need" presented a crossover between 'EastEnders' and 'Doctor Who' back in 1993 which I consider canon. (Even if some 2013 aspect of Albert Square was later contradicted by 'EastEnders' itself, I'm fairly certain a splainin could be found for it.) That "Dimensions In Time" vignette serves as proof that 'EastEnders' and 'Doctor Who' can share the same TV dimension.
However, now comes word that 'EastEnders' filmed a few scenes at a fictional 'Doctor Who' exhibit supposedly at St. Paul's Cathedral. Apparently as part of their honeymoon(?), Bradley and Stacey visited "Doctor Who - The Time Lord Revisited" because Bradley is something of a 'Who' nut. When the scenes are broadcast sometime in the new year, audiences will see the couple alongside the TARDIS, Cybermen, a Dalek and even K-9.
So even though we can get around mentions of 'EastEnders' in 'Doctor Who', it gets a bit trickier if 'Doctor Who' gets mentioned in 'EastEnders' without losing the prime-time soaper to yet another TV dimension.
(Sounds like that old chocolate/peanut butter argument from the Reese's blipverts: "Hey! You got 'EastEnders' in my 'Doctor Who'!")
It's not that hard to conjure up a splainin, and in fact I've done it in the past - most references to 'Doctor Who' within another TV show which should be sharing the same reality are about the movies which starred Peter Cushing back in the 1960s. And for alls we know, there have been movies since then about "Doctor Who" in Toobworld featuring other actors. (This gives us an out in case specific actors are named.)
As to why there would be a movie about the Doctor, here's my theory: Some movie producer heard rumors of the Doctor's existence (It's not like he was hiding himself back when he visited London in the sixties and seventies.) and decided to cash in by making a movie about him. Of course, he didn't know all the specific details about the mysterious stranger and that's why the character is actually named "Doctor Who" in the movies. But he did know enough that he was able to get right such details as the Doctor zipping about in the TARDIS and having a grand-daughter (although he has two in the movie).
No need for Zonk-splainin when it comes to the presence of the Cybermen, K-9 and the Dalek at this exhibit because all of them would have been known to the general public of London due to past invasions or other encounters.
So making references to 'Doctor Who' as fiction within the world of Walford isn't a Zonk. Referring to 'EastEnders' as a soap opera while on board the TARDIS is.
Got it? Good.