The listing concerning Andrews & Arnold and their various offerings in the ISPs section could do with being updated and expanded.
They basically have 3 (or 3.5) different offerings.
* The Home::1 offering is for non-business users only. You get a certain amount of download allowance, you can buy extra if you wish. Example: 100GB download per month is £25. Upload is free iirc.
* Secondly there is an Office::1 service which is a high availability service with a firebrick and two or three lines.
*A variant on this (hence the .5) is "Office::1 Unlimited", a slowed-down FTTC service with truly unlimited usage, at fixed cost. You can download flat out 24-hours a day and you are charged enough to pay for this, but since the data rate is not high, the total amount of data that can be transferred in one month is not totally ridiculous.
* The traditional units-based tariff is where you buy units in advance, one unit represents a download allowance of so-many GB, depending on time of day, weekend or workday and on the type of connection, for example BTW 20CN ADSL being the most expensive in office hours compared with 21CN. Night-time usages 02:00-06:00 currently is charged at 1 unit = 1000 GB, weekend evening usage is 50 GB per unit, office hours = 1.25 GB per unit for 2.5 GB per unit depending on the type of connection. One unit costs £3.90, iirc.
So as you can see there is strong incentive to use as much off-peak as you can.if your usage goes over the number of units paid for in advance, you are charged for the access at a slightly higher rate. If your units are not used up during one month, then the remainder is carried over to the next month. This is the service I use myself.