Visit 192.com (see Reference). This is a free online UK phone book. Enter a business or person's name and it will give you a list of possible phone numbers in the results.
Enter in the subject's name and/or part of an address in the fields provided. The more information you provide, the more your results will be narrowed down.
Press the "Search" button when you're ready to conduct your search. On the following page, you will be shown a list of matching names and phone numbers. You may now select the correct party and make your call.
