i'm not too sure on a snmall turbo, on the t34, the actual probe goes in the turbo housing itself so isn't affected by any aftermarket exhaust.

it will already be lambda controlled, fitting one to acar that didnt have one inthe first place wont do much good as the ecu woun't use it, and besides, a car that was supposed to have a cat WILL NOT pass a mot without one regardless of how well the engine is running. you need to find a friendly mot station that would hahmmmm , wave the emisions probe up the exhaust of a micra on the next ramp along...