Any self-respecting filter should be able to sort that out...
Well we'll see. I'm not convinced that every £5 WiFi NIC comes with a half decent front end filter.
...and it's not like wifi is below the noise threshold like GPS is,
Ah, a classic mistake. If an RF front end gets saturated by a high power jamming signal, the receiver won't be able to pick up any other signal at all regardless of whether or not it's above or below whatever one defines as being the noise floor. A front end amplifier that's clipping won't pass anything worth a damn.
So if a WiFi NIC has a poor quality RF front end (a distinct possibility) and is co-located with a 4G phone (effectively a certainty in this day and age) pushing out a good 0.5W of RF, it's by no means certain that the NIC won't get saturated and crap out.
I'm sure OFCOM has thought about it, or at least I hope so...