Aircraft such as the B777 are tested against HIRF (High Intensity Radio Frequency) and critical areas such as the Main Equipment Centre of this aircraft is shielded against it (you only have to look at the SRM for this).
Systems such as flight controls and other rated as critcal are qualified against RF levels up to 200 volts per metre and taking into account the far field square law for RF attenuation (as you double the distance, you half the power), you would need something big and powerful to affect an aircraft at any altitude. For example, the RADAR tower at LHR will be pushing out a fair bit of energy and this is less than a few hundred metres away from aircraft.
This is not RFI/EMI/EMC related incident IMHO