Russell Keane <Russell(dot)Keane(at)inps(dot)co(dot)uk> writes:
> Sorry, I should've added that in the original description.
> I have an index on search_key and it's never used.
Did you pay attention to the point about the nondefault operator class?
If the LIKE pattern is left-anchored and as selective as your example
implies, the planner certainly ought to try to use a compatible index.
regards, tom lane