Depends how far from your exchange you are, condition of the phone line, amount of extension cabling in your house, time of day. These will all affect what you actually get. What does click here say you should be able to get?
I know you said what you got, but that is only relevant to what your ISP says you should get. The phrase 'Up to..' is frequently used and is very missleading for most people. If your estimated speed (from the link) is 2Mb and you're getting 1Mb, that could well be about right (depending on the time of day and how many other people are on line in your area). My estimate is for 6.5 and I rarely actually get more than 4.
You need to post your Stats from the router. You will get something like mine:
ADSL Line Downstream Connection Speed 19639 kbps Line Attenuation 17.5 db Noise Margin 6.3 db
You can take a good guess from the Noise Margin about how much more speed is available to you. If you have a Noise Margin above 7 db then their may be more speed capacity in your line however that depends upon some other factors but it's a good place to start.