My car has failed MOT on emissions and I dont know what to change, CAT or Lambda? The readings are below:

Fast Idle test:

Engine speed: 2500 - 3000rpm

CO: 0.68% - Fail

HC: 120ppm - Pass

Lambda 1.020 - Pass

Second Fast Idle test:

Engine speed: 2500 - 3000rpm

CO: 2.52% - Fail

HC: 495ppm - Fail

Lambda 0.946 - Fail

Natural Idle test

Engine speed: 450 - 1500rpm

CO: 0.50% - Pass

Thanks in advance!