Here are some things to try:
Check the electoral rolls, either online (search Google) or in the library.
Post on the Topics/Lost Family & Friends board about the relatives you seek. Best to limit each post to a single surname. Be sure to mention the location(s) in which they may live.
Post on the relevant surname boards. Provide the latest information you have and asl for help finding descendants.
Place a small ad in local newspapers, either in print or online. For example, the Manchester Evening News has an "In Touch" section where people post about lost friends and family. See http://www.manchestereveningnews.co.uk/community/in_touch/
Use Google to search for online telephone directories in your areas of interest. Obtain the names and addresses of those you think may be related to you and write to them. Be sure to carefully explain that you are just trying to connect with possible family and be sure to enclose a stamped, self-addressed envelope so that the person can reply.
Hope that helps a little.