The intercombination a 3 Π−X 1 Σ + Cameron system of carbon monoxide has been computationally studied in the framework of multi-reference Fock space coupled cluster method with the use of generalized relativistic pseudopotential model for the effective introducing the relativity in all-electron correlation treatment. The extremely weak a 3 Π Ω=0 + ,1 −X 1 Σ + transition probabilities and radiative lifetimes of the metastable a 3 Π state were calculated and compared with their previous theoretical and experimental counterparts. The impact of a presumable variation of the fine structure constant α = e 2 / c on transition strength of the Cameron system has been numerically evaluated as well.