Petrol Engine Emissions

My friends Freelander has just failed it's MOT on emission. Other than the usual stuff that I will be checking for them like.

The air filter restricting the engine from breathing, clean it replace it.
Spark plugs need adjustment / replacement.
Putting in a fuel adertive and thrashing it up the bypass and back a few times to try and clean the injectors.

My question is:
Is there any way to adjust the mixture??

No,it is supposed to be running closed loop off the Oxygen sensor.If its showing high on emissions,forget the injector cleaner,air filter and snake oil.Instead look at the plugs,leads,cap and rotor.Then go for checking that the Oxygen sensor is capable of switching, then check that the Cat is still in one piece and working.

How do I check that the Oxygen sensor is capable of switching? What do you do if it's not?

Can some one answer the above question please;

The MOT centre should have given you a print-out from the gas analyser: can you advise:

HC ppm level

CO %

Lambda reading

Hello Dann

I can't at present as it's not my car it belongs to a lady I know and I don't have that information at present.