Andrew - Fault was reported to BT hours ago. I notice your reluctance in answering my question!

I have no answer to the question, since I'd like to actually do this to test it rather than go by theory of whether the jumper filter will isolate the exchange side issue enough to ensure that the broadband is not affected

If I was to think logically about an answer then yes. If there was a short on the copper before the cab then it could place noise on the line that might interfere with the broadband signal that is added at the cab. I guess it depends on what the DSLAM in the cab can do about removing the noise in the broadband frequencies.

Thanks Ian72 - I'm just looking for answers.

BT Diags update page now says "Exchange Fault"

It'll be interesting to see if the exchange fix delivers a lasting BB solution?