That website offers pretty much everything you need to know in regards to your home connection to the nearest exchange, what capabilities the exchange offers technology wise and speed wise etc. Pretty nice website for information within the UK. Go to exchange search, hit in the telephone number of the house in question, click on the exchange name that the house is connected to and it should display all the information you need to know.
:: Edit ::
Click on the availability feature and enter your phone number in there. It'll tell you all of the ISP's that are available to that number.
Although for us in the UK, it seems the only company that does offer Internet access on the cable infrastructure at the moment is Virgin. Wonder when they will start renting it out like BT did with their phone line infrastructure.