A funny thing about Rose, Aliens of London & World War Three is that they were directed by a guy who just didn't really 'get' what Doctor Who 2005 was going to be, and a lot of the farting ADR and stuff came from him. He basically thought the tone was going to skew more younger than family. A lot of those episodes play like Sarah Jane Adventures later would but with darker scripts, and that's the mistake, really. Like, the fact the Slitheen had an eggy fart smell as a give away and sometimes made fart noises was indeed in the script, but it was the director who played it a lot more for laughs and added in a lot of additional farting after the fact in the edit. You can see this in Boom Town, later, where one is played with that stuff toned right back. A lot of people think that's because of a backlash to AOL/WW3, but Boom Town was in the can long before those episodes aired; it was just delivered closer to how it was scripted.
Same sort of thing for, say, when Mickey is 'eaten' by the bin in 'Rose' - the way that's scripted, if you read the script, is for it to be relatively harrowing/nasty, it's meant to be scary for kids. But the director shot it in a relatively flat way, directed Clarke to play it slapstick (there's also Mickey dancing for no reason in the opening montage; you might notice the portrayal of Mickey later on and then in Series 2 is very different and more grounded) and even added the bin burping, which was not a scripted moment at all. Direction can do a lot to a script.
That Director is also the one who had screaming rows on set with Eccleston and all that, so, welp, yeah. He's the only one from Series 1 who never ever returned to the show, as well. RTD later expressed regret on a DVD commentary he hadn't spoken up more about the amount of the farting and the way it was being played, but obviously it was their very first edits and everybody was finding their footing.
I still actually think on paper Aliens of London/World War Three is the best 'Earth Invasion' story they've done since 2005. Incredibly tight scripts - the execution is just lacking.