What ytour BB can run at is the theoretical maximum. What it actually does run at will vary all the time, depending on what's being sent from where, how busy the serving site is, how busy the lines are, how well your system can handle the speed etc etc.
Having said all that, 2Mbits/sec should equate to around 240Kbytes/sec. The speed tests should show what it is doing. If it looks substantially wrong over several tests at different times, then you should contact your ISP.
Note this is only for incoming data. For outgoing the speed is very much less - I don't actually know for Tiscali, but I would imagine 256Kbits/sec. (anyone who actually knows can correct this figure please)