  In this paper we continue to pursue a goal of finding an effective theory for
high energy interaction in QCD based on the colour dipole approach, for which
the BFKL Pomeron Calculus gives a low energy limit. The key problem, that we
try to solve in this paper is the probabilistic interpretation of the BFKL
Pomeron Calculus in terms of the colourless dipoles and their interactions. We
demonstrate that the BFKL Pomeron Calculus has two equivalent descriptions :
(i) one is the generating functional which gives a clear probabilistic
interpretation of the processes of high energy scattering and also provides a
Hamiltonian-like description of the system of interacting dipoles; (ii) the
second is the Langevin equation with a specific noise term which is rather
complicated. We found that at high energies this Langevin equation can be
reduced to the Langevin equation for directed percolation in the momentum space
if the impact parameter is large, namely, $b>> 1/k$, where $k$ is the
transverse momentum of a dipole. Unfortunately, this simplified form of
Langevin equation is not applicable for summation of Pomeron loops, where one
integrates over all possible values of impact parameter. We show that the BFKL
Pomeron calculus with two vertices (splitting $P\to P+P$ and merging $P+P\to P$
of Pomerons) can be interpreted as a system of colourless dipoles with two
processes: the decay of one dipole into two and the merging of two dipoles into
one dipole. However, a number of assumptions we have to make on the way to
simplify the noise term in the Langevin equation and/or to apply the
probabilistic interpretation, therefore, we can consider both of these
approaches in the present form only as the QCD motivated models.
