Let G be a finite group and p be a prime. We study the kernel of the map,
between the Burnside ring of G and the Grothendieck ring of
Fp[G]-modules, taking a G-set to its associated permutation
module. We are able, for all finite groups, to classify the primitive quotient
of the kernel; that is for each G, the kernel modulo elements coming from the
kernel for proper subquotients of G. We are able to identify exactly which
groups have non-trivial primitive quotient and we give generators for the
primitive quotient in the soluble case