Thankyou very much for your help. Back to normal. I will monitor and when noise on line I will contact plusnet to fix, seems very intermittent. But dlm does not seem to automatically recover speed after noise has gone away.
Things do not quite work like that! The DLM will seek to maintain a stable connection, if that means raising the TARTGET SNRM (lowering the speed) then it gets adjusted until the connection remains stable. Whilst the connection remains not-disconnected, the speed will certainly remain unchanged. If there has been a disconnection for some reason there is some possibility that the DLM might improve the TARGET SNRM, but there is no assurance that will happen without a line reset.
If there is repeated need for a line reset, then that is indicative of a fault on the line or with consumer side wiring or equipment.