  The processes $e^{+}e^{-} \to 4f(\gamma)$ mediated by W-pair (and single)
production are considered in the framework of the modified perturbation theory,
based on the expansion of probability in powers of the coupling constant
instead of amplitude. A full set of one-loop corrections to cross-section, and
two-loop corrections to self-energy of unstable particles are completely taken
into consideration. It is shown that the manifestly non-factorizable
corrections do not make contributions into the next-to-leading-order
approximation. Moreover, the colour reconnection does not make contributions
within this precision, either. The rest of the corrections together with the
leading-order contribution provide the gauge-invariant description of the
processes.

High Energy Physics - Phenomenology