Tilt sensor for the alarm is in the left side cargo compartment behind the access panel.
I beleive MINIs had an inertia switch (for fuel cutoff if impacted) only up to 09/2002.
In that case, it's near the strut tower, outboard of the brake resevoir. There's a pic on
page 16-17 of MINI Cooper 2002>2006 Cooper, Cooper S Diagnosis Without Guesswork.
Not sure of where the alarm relay is offhand. Regarding alarm switch, which switch do you mean?
Another pic here: http://new.minimania.com/part/NME771...p---R50-Cooper