Well I did some tests last night as the fix should have been done on the 30th, unfortunately it either hasn't been done or it didn't work.
I will wait to hear back as I was promised a call today at some point.
It wouldn't even run the further diagnostics for the second test I did where the speed had dropped even further.
So it looks like my issue has been fixed after a few weeks. Tests run at 9:30 last night show pretty much full speed so I'm happy again. Will keep an eye on it though.
Thanks to the Mods on here keeping me up to date with the issue.