Catalytic Converter Light VX Vectra late 2002 1.8

[rossi1009]

Just wondering if someone could give a bit of advice, just bought a late 2002 1.8 petrol Vecta now for the last 2 days the Catalytic Converter light has come on and the engine is losing power between 500 and 2000 revs. The engine is chugging like it is miss-firing or as if there is some dirty petrol in the car but i've been putting BP Premium into it. Is this an problem that I will have to take to the garage or is there something someone with very basic car mechanics can sort