That is a bit tight.
Assuming that your Mini uses imperial nuts and bolts:-
Get hold of something like a scrap of thinish 9 inch square plywood.
Drill a 5/16" hole in a corner and do up a 5/16" nut and bolt through it.
Place your ring spanner on the nut and draw either side of the spanner.
Move the spanner round 1/12th and draw again.
Rummage through your friends tool boxes or go to hardware stores and find a spanner that fits on the nut, half way between the two drawings. Better still, you might find two spanners that fits a third from either drawing.
Two (or three) slightly different spanners should enable you to rotate the nut in that confined space.
Pull a bit of string back and forth in the threads above the nut to remove crudd, and when loose, it might be only finger tight.