Re: This seems similar to the global snooping (encryption) issue.
In the US, we call the principle "Fruit of the Poisoned Tree". If evidence was obtained illegally, then ANY subsequent evidence that the one piece led to must be thrown out as well. Meaning, if the tainted evidence was the linchpin of your case, you just lost your case. Now, if you have other evidence to present, you can still present it, but because juries cannot UN-learn something they weren't supposed to learn (thus creating uncorrectable bias and thus tainting the entire jury), illegal evidence can present grounds for a mistrial.