You've got a 2 megabit, not megabyte, connection, zc1. Therefore, a 250KBs download is a pretty decent speed.
There are all sorts of speed tests: one of the best for download speed is
Robin Walker's speed test. Because it's on the ntl network, it doesn't tend to suffer as much as some speed tests can from internet conditions.
Also, if you're on a cable modem rather than a settop box, you may be able to check the settings by directing your browser to
http://192.168.100.1/ and entering 'root' as username and password. Go to the configuration page (on my NTL: 250 modem it's the Operation Confiuration page) and see what it says there. If you're on a 2Mb connection, it should say something like: Maximum Downstream Data Rate : 2048000 Maximum Upstream Data Rate : 200000. This is your connection speed, not how good that connection is to remote sites, which will determine your actual download speeds.
You can find more information on querying cable modem and settop box settings at
Robin Walker's Cable Modem Troubleshooting Tips page. One last word of warning: don't try to change anything in your modem settings. Just use them for diagnosis.