First, it is not a police box, but a phone booth :P But most importantly, it is a parody, which stems from another show the guy playing Inspector Spacetime starred in: Community. One of the shows characters is a huge geek and into TV-Shows and Films. After his favourite TV-Show is cancelled, so he needs a new one. One of his friends introduces him to "Inspector Spacetime, a British sci-fi show that airs since 1963". So in community they do a reference/homage to Doctor Who. The guy who plays the Inspector here also played it in the little snippets one could see on "Community". So it is more of a meta-thingy than an actual rip-off.