"Of course, BT could always be telling the truth and exceeding the 100mW @ 2.4GHz legal limit; in which case, they also lose."
Disclaimer: I hate BT with a passion and will happily discourage anyone from using their services.
BT aren't doing anything illegal AFAIK, just providing better equipment:
-. 3x3n/4x4ac radios with beam forming when their competitors are using 2x2n/3x3ac radios.
- better antenna designs than their competitors
- CPU/memory capable of supporting the router/wifi functions without overheating or experiencing performance bottlenecks
- software that allows most functions to work as designed
TL;DR: unlike their competitors, BT's HomeHub software and hardware was not complete shit.
The details of the tests are here if you want to compare this for yourself:
Effectively, BT were PROBABLY right with their claim to have "the most powerful wifi of major broadband providers" based on the testing results, however BT's test did not cover all forms of interference (I'm guessing DECT phones as the likely options that have been missed - the other causes such as microwave ovens, dodgy baby monitors, electrical cabling issues etc are faults that should really be addressed). The ASA's statement isn't clear on the reason which makes it hard to disprove:
"We noted BT had tested for both Wi-Fi and Bluetooth interference. However, there were other forms of non-Wi-Fi interference common in many households beyond Bluetooth for which BT had not tested."
The thing that annoys me most about the ruling is that almost any Virgin Superhub user will tell you that anything is better than a Superhub (see Intel SoC issues, known crap software, inferior wifi hardware, Virgin support).