Larkin doesn't give us a super-obvious setting for this one. The speaker never declares he's here or there, inside or out. But there are some aspects of the poem that give us some sense of place.
There are some words that put us in an outdoors-y frame of mind: "pitchfork" (trust us, not a good inside tool) "windfalls," "toads." But the poem's overall feeling is interior. Here's why:
Like we discussed in the "Sound Check" section, the poem has a very talk-y feel. (There's extra credit if you can remember the term for that talk-y tone. If you said "colloquial," ten points for Gryffindor! Er, sorry—just award yourself a bazillion Shmoop points.) This colloquial sound, coupled with the fact that the speaker is going on and on about work and getting a little more serious and emotional as the poem nears the end, reminds us of a guy sitting at the bar, pouring out his troubles to the bartender. Larkin sat at a bar or two in his time, so he certainly would have had an ear for this kind of talk.
At the end of the day, though, this back and forth is really taking place inside the speaker's head. At first he's wrestling with that toad, but then becomes resigned to defeat. Work does a big, warty bellyflop on his spirit and pins him for the count—bummer.