I was also advised NOT to call them back before the engineer arrives regarding this problem as it would wipe all their records and ticket history and it would all have to start from scratch. Never heard that one before!
When I had speed degradation in the evenings recently (down to 1Meg or less from 7+day time speeds) the engineer did various checks and fitted a proper adsl master skt and said he was certain that it was an exchange problem which it was. when I run the call centre a week later to see what was happening they said they would have to start the whole process again. An engineer arrived...................................