My Octy mk1 vrs failed last years mot on emissions , replacing the cat cured the problem or so i thought, this year the same happened . The fast idle reading was 3ppm when it should be 0.19ppm I can't afford a new cat every 12 months so if anyone has had similar problems or knows of a cure i would be greatful for any help you can give. 

thanks

Doesn't the cat u had fitted have a warranty on it?