UPDATE for you all
an LL1 engineer came out and found a leg was down and no dial-tone, he said he found a bad joint and repaired it but also that my run was on aluminium... now with all the information at hand and especially the 12-4am downtime, raise in Line Attenuation, loss of 10Mb speed and no-dial-tone afterwards indicates to me that an engineer on the 28th July has moved my pair onto another and this pair is Aluminium (hence the speed loss) - the engineer said he couldn't do anything about it as they dont guarantee speed, only stability.
he got even lower speed on his JDSU (59Mb) so he did reset DLM which turned Fastpath ON and bumped it up JUST past my MALS (Minimum Access Line Speed) which means I can't roll back to 40Mb, however, if DLM turns Fastpath OFF I get 59-64Mb which is below my MALS - im happy enough with the speed, its just annoying and frustrating knowing what's likely to have happened but not being able to prove it nor get it resolved, especially when ive had 8 months of at circa 74-79Mb for it to drop to 64-69Mb overnight.