It would be easiest to help if you would provide some point of reference or a copy of the document that contains the abbreviation.
Failing that, you could use GENUKI's Gazetteer at
http://www.genuki.org.uk/cgi-bin/gazIn the first field, Place name, enter an "L" and change Search type to "Word beginning" and then be prepared to wait a minute or two. You'll be presented with a list of just about every location in the UK beginning with an L and you can then search the list for a location that may have been abbreviated as LB.