The real reasons
Oh FF Sake! BT blaming interference and their solution is "filter it out". NO! Stop the interference from getting in in the first place. What a bunch of muppets they are.
1)Start using shielded, screened cable for data transmission. Fundamentally, the cabling we all use for connecting slave/extension telephone sockets was never designed for high speed data transmission, come to that, it was never designed for data transmission period! It was designed for low bandwidth (up to 4KHz) analogue voice transmission.
2) BT, the reason we have poor internet connection speeds it because you t**ssers insist on using the local loop made of poor quality unshielded twisted pair, that again, wasn't ever intended to transmit high speed data.
Stop blaming anything, everything else for the low data rates and take a look at your own s**t infrastructure.
Many things radiate radiowaves and that's permitted by law. Susceptibility to that RF interference is governed by laws. It's a fact of life that the air is full of RF crap, BT should stop blaming poor ADSL performance on RF interference and they should be proactive and take measures to ensure their infrastructure isn't susceptible to it: ie. it's their f***ng problem.
How about some decent f**ng cable designed for data transmission?
Makes me wonder if BT know anything about data transmission at all. Funny, their Martlesham Heath research establishment is full of graduate Electronic Engineers.