In this paper, a safety assessment of the General Method (GM) in Eurocode 1993–1-1:2005 is carried out. The GM covers the stability verification of steel structures subjected to compression and/or bending even in cases where the structures have irregular shape, complex load and support conditions. Several research papers dealt with the accuracy of the GM, but within the method, all of them used the Ayrton–Perry formula type standard reduction factors calibrated for the fundamental (flexural and lateral-torsional) buckling modes. These studies compared the results of the GM to the results of the geometrically and materially nonlinear analysis with imperfections (GMNIA) applying characteristic numerical models. In this paper, firstly the exact imperfection factors of fundamental buckling modes are calculated with GMNIA, after that these factors are used within the GM. This way the effect of the inaccuracy of the standard calibrations is excluded, and the real accuracy of the GM will be reflected in the results. This study covers the fundamental case of coupled flexural and lateral-torsional buckling modes in case of hot-rolled IPE and H-type cross-sections.