OK....so there I was, digging over the allotment, getting ahead, making trenches and filling with green waste for next years beans - suddenly, a (big, giant, ugly) rat appears out of nowhere and scuttles away

One week later, I find a tunnel in the side of the trench, and without doubt, the rat has decided to make a home for himself.... what should I do?

will he cause problems?
should I leave well alone?
poke and annoy until he decides to re-house himself?
attempt to kill (how??!!)

anyone got any bright ideas?