If you want to have any cellular functions apart from placing emergency calls, you have to have an actual cellular plan through a carrier.
Picture it this way: If you buy a land line phone for your house, take it out of the box, program speed dials, and set it on your table without plugging it into a phone line, you won't be able to receive any phone calls. Your cell phone is simply a tablet until you activate a cellular plan through your carrier for it.
Also, the ability to place emergency calls is a feature on all cell phones that is not dependent on carriers.
Here is a list of UK Carriers.