Most services come through a BT line. If there is nothing in place now, this will cost £125 to install plus £10.50 per month (maybe there is a minimum contract length?). You can then choose for the hundreds of internet provides and call discounters listed on this site and elsewhere.
Without going for a BT line, the other options are cable and mobile. The main cable provider is Virgin but there may be other local options.
Mobile broadband is quite flexible and may suit a shorter or non-permanent stay. You can either buy the dongle and pay for each month that you use it or you can sign up to a contract. Three offer the best prices but they also have the poorest coverage. I don't have a BT line as they don't cover my city and I recently opted for Vodafone mobile - the connection is not as good as a landline but it is very flexible and can be used at any address.