Congratulations Octal ! Someone who appreciates that there are grades of ferrite with different RF properties.
Thanks, I think 31 mix might have been a better choice, but 43 was all I had which is intended for the higher HF bands, but it seems to have done the job for me.
Here is a link to a somewhat old document that has relevance to xDSL and "Top Band".
I have built one of those and they do indeed work, but the cut-off is about 1.7MHz, so the download speed is reduced by about 2 or 3meg as I'm on ADSL2+ which has an upper frequency of 2.2MHz, with the ferrite I at least just lose a few tones around Top Band and the speed is only reduced by a few hundred K.
I've still got a notch at 909kHz which comes from the Brookmans Park transmitter, it's about 15 miles away, I can just see the top of the main mast from here, so it's a strong signal, the ferrite hasn't changed that, so it's probably not coming in on common mode.