Well, what a struggle that was! I powered down my router overnight on 28-29/09. It's something I do about once per month. Next morning (29/09) the router synced with the exchange at full speed (8128 kb/s before you ask) but wouldn't authenticate. Same story every day since.
COMS support suggested
a) power off, wait anything from 5 to 20 minutes (the time varied depending on who I spoke with)
b) reset the router to factory setting then re-enter my userid & password followed by power off/on etc.
c) reset my userid
d) they would dispatch an BT engineer to check my wiring & equipment. This I refused unless they paid any resulting fee
Eventually, after many iterations of a) thru c) they suggested yet another userid! Bingo! I'm back online!
Nine (9) days offline because someone, presumably at COMS, messed up my RADIUS profile.
Needless to say, I'm now looking for another ISP. Just waiting for the MAC