Obviously you didn't read my original post thoroughly, I shouldn't have to point out the difference between quality and speed (but it appears that I have to anyway).
I don't see how a minuscule increase in sync rate from a master filter could prevent my speeds dropping from 1.8mbps to 0.18mbps every night and my ping to Auckland from trying to break the 4 second barrier.
If we pop my attenuation into a calculator that assumes no wiring issues it produces a distance of 4.2Km. As the distance between my house and the exchange is probably over that distance, would it be safe to assume that my wiring isn't at fault and the purchase of an expensive filter unnecessary?
I pay my ISP to provide a service which they have done without fault for 5 years but now suddenly can't.
Would a new customer coming onto a BUBA exchange be able to turn a stable connection into a wildly unstable one in just a night?
My new modem has arrived and tonight I will do the mother of all tests.
I'll update this thread with what I find.