I posted this as a reply to an existing thread but thought I'd raise a new topic as it may help someone.
We've been having occasional line drops and terrible packet loss at random times although being worse in the evening. I had tried several modems including an Asus N55u which although has great functionality is very tempremental / fussy on ADSL line quality.
We had a BT engineer visit and he performed a thorough test of our installation and found nothing and then reported the dreaded REIN as the culprit without actually identifying any particular device.
I was very dubious as I thought it was a copout - but I had to conduct my own tests by trial and error.
To cut a long story short, my problem was down to the TP Link home plugs on the mains network.
After removing all the sockets my troubles have disappeared! 8)
Now have to install ethernet but at least our broadband is steady now.
I would be very interested to hear if anyone else has this issue.