  We evaluate the expected level of foreground contamination to the cosmic
microwave background (CMB) polarised radiation, focusing on the diffuse
emission from our own Galaxy. In particular, we perform a first attempt to
simulate an all sky template of polarised emission from thermal dust. This
study indicates that the foreground contamination to CMB $B$ modes is likely to
be relevant on all frequencies, and even at high Galactic latitudes. We review
the recent developments in the design of data analysis techniques dedicated to
the separation of CMB and foreground emissions in multi-frequency observations,
exploiting their statistical independence. We argue that the high quality and
detail of the present CMB observations represent an almost ideal statistical
dataset where these algorithms can operate with excellent performance. We
explicitly show that the recovery of CMB $B$ modes is possible even if they are
well below the foreground level, working at the arcmin. resolution at an almost
null computational cost. This capability well represents the great potentiality
of these new data analysis techniques, which should be seriously taken into
account for implementation in present and future CMB observations.
