  We investigate the evolution of non-linear density perturbations by taking
into account the effects of deviations from spherical symmetry of a system.
Starting from the standard spherical top hat model in which these effects are
ignored, we introduce a physically motivated closure condition which specifies
the dependence of the additional terms on the density contrast, $\delta$. The
modified equation can be used to model the behaviour of an overdense region
over a sufficiently large range of $\delta$. The key new idea is a Taylor
series expansion in ($1/\delta$) to model the non-linear epoch. We show that
the modified equations quite generically lead to the formation of stable
structures in which the gravitational collapse is halted at around the virial
radius. The analysis also allows us to connect up the behaviour of individual
overdense regions with the non-linear scaling relations satisfied by the two
point correlation function.
