It's a model line that came into use in the late 1930s when the London factory opened. They the used that line name on and off up to today - 2016 had a new high grade Dublin & London line.
It can, in conjunction with other clues, narrow date ranges but not by much.
Peterson did also reverse the name - London & Dublin - for pipes made in the London factory. The London factory closed in the early 1960s.