There are a few ways you can audit your connection.
Start by looking here: http://www.speedtest.btwholesale.com/ It is recommended that you complete this test with a wired connection from your computer. This will not work correctly on a mobile device like a phone or tablet.
Once you have the speeds noted down the next step is here: https://www.btwholesale.com/adslchecker/ Just type in your telephone number and click submit. Give it a moment and you should be presented with table showing you what you are able to get in both best and lowest.
Compare this with your notes from the first test and compare.
Please note that high demand times do effect the results, so best to try this before 4pm or after 10pm.
Below is a good example of how a connection from the green cabinet degrades over distance.