i want a decat but the lambda sensor/EML situation bothers me as im not 100% on wether it would run right if its not getting the correct lambda reading?
Taking out the rear lambda sensor shouldn't affect how the car runs, as it's the readings from the front sensor (the one before the cat) that is used to make fuelling decisions.
The rear sensor is only there as a requirement of the EOBD legislation, as the car has to be able to monitor the performance of the cat. (The vales before and after the cat are compared).
If you remove the rear sensor the Check Engine Light should come on, but it's usually treated as a minor fault by the ECU and doesn't prompt limp mode.
Driving round with the light on permanently isn't wise though, as you won't know if something more serious goes wrong (as you won't see the light come on for the new fault).
Bear in mind that to get through a 2012 MOT, even if your emissions are ok without the cat, the cat still has to be fitted, or the car will fail for the cat being missing.
If you're willing to swap the cat back in for the test every year and go ahead, you can get lambda simulators to plug in in place of the rear sensor, to fool the car into thinking the sensor is still there.