I had a very similar thing happen to me last year with the HH3 but it was the Upload was being restricted, It should have been around 16mb and it was holding mine down to around 9.5mb.
In the end I bought a Western Digital n750 dual Band router when they were on offer in PC World for about £17 (hated the Home Hub anyway!) and hey presto my upload was back to 16mb!.
When I switched from BT to Plusnet in December I refused all offers of a new router, kept my WD n750 and haven't had any problems. In fact since I got my n750 my connection has increased from 60/16 to 67/17, not a huge jump but at least it's stable.
I haven't ever had a decent router supplied by any ISP since ADSL started, their main concern with the equipment they supply these days is locking it down so that you can't use any other firmares rather than good reliable performance.