I don't think the program was very well balanced - if they had played all the coughs at the correct volume, would it have seemed that blatant? Also, there was no testimony from the accused...
Having said that, he does look pretty damn guilty and seemed to be an appalling actor, grasping at straws. The "cough, no!" one just seemed ridiculous as did the way he chose the Craig David (bo!) answer.
Also, wifey's cough seemed to be blatantly not real too.
It goes to show you though, that if they'd come up with a less blatant method of cheating and chosen somebody who wasn't such a crap actor, then they might have got away with it. I'm sure as well, if you used some crafty electronics, you could come up with something that would let you recieve a 1 to 4 signal, and would get through the searches....