LLU means Local Loop Unbundled, which means the ISP has it's own equipment in the exchange so is not limited to retailing a BT Wholesale product.
Your exchange hasn't got any

.
In particular it hasn't got Sky LLU, which is a good service. The BT-based Sky Connect is what you hear the horror stories about, and it hasn't improved. Stay away.
50GB per month is difficult at budget prices, but the suggestions below are good ISPs and about the only ones I would recommend.
I think the best ISP for you would be
AAISP. The daytime allowance Mon-Fri is tiny but as well as the large off-peak allowance there is an overnight unmetered period.
Next down I suggest
vivaciti Surfwise 75. Ignore the Family packages next to it, and the LLU on the right. The Family packages are supplied by Entanet and used to be excellent value for money. That is no longer the case as they suffer badly from Entanet over-subscription - mainly customers who haven't steeled themselves up to jump since it went downhill. The LLU you cannot get, as above.
See
these comparisons. As vivaciti is a reseller it doesn't appear on the selection list, but their Family packages come in the Entanet bars. Surfwise 75 would be well above that but not as high as AAISP.
Which ISP are you with at the moment?
Edited by RobertoS (Fri 04-Sep-09 21:07:13)