I just recently moved from Australia to the UK and that's one of the interesting things I noticed. In the UK you pay for the speed of your connection rather than how much you can download. So as others are saying, the 10Mb is referring to a 10Mbit connection speed. You can download as much as you want.
In Australia, the speed is basically always "ADSL2+" which means a theoretical maximum of about 20Mbit but in practice is highly dependant on how far away you live from the telephone exchange and the quality of the lines in your house etc. I never got speeds anything like 20Mbit and I lived close to the center of town in Melbourne (~3.5mil population). When you go over your download limit (typically 10-50gb), the speed is "shaped" or "capped" to something near dialup modem speeds.