  The infrared problem of the effective action in 2D is discussed in the
framework of the Covariant Perturbation Theory. The divergences are regularised
by a mass and the leading term is evaluated up to the third order of
perturbation theory. A summation scheme is proposed which isolates the
divergences from the finite part of the series and results in a single term.
The latter turns out to be equivalent to the coupling to a certain classical
external field. This suggests a renormalisation by factorisation.
