Sure, in the same way that it's painfully obvious any packet using the expression "shake it off" is an infringement of copyright on a well-known pop song.
Not only that, but to make this actually stand up in court against a technically competent argument by the other side, you would probably need to ensure that the iPlayer always sends some unusual and therefore distinctive sequence of packet sizes (which is far from a trivial issue if you're serving via HTML5 video, for example) so you have some sort of signature to look for. Then you would need to be able to recognise that signature in real world wireless traffic, in the presence of encryption, fragmentation, control traffic, and arbitrary other data being transferred between the same systems at the same time.
Good luck with that. It would be like looking for needles in a haystack, when each needle was made by cutting and drying vegetable matter, and each needle had similar but slightly varying dimensions like hay, and you didn't know how many needles, if any, were actually there in the first place.