[exim] drop emails by subject - should be simple

Hi All,

I'm trying to add a *simple* SPAM filter rule to exim:

  drop    message   = Subject is know SPAM email, ignoring
          log_message = Message dropped because of know SPAM Subject
          condition = ${if >{${strlen:$h_subject:}}{20}{yes}{no}}
      condition = 
${lookup{"$h_subject:"}lsearch{/etc/exim/lists/subject.droplist}{yes}{no}}

I have the following:

[root@ollie2 lists]# cat subject.droplist
This is a test subject
[root@ollie2 lists]#


However, when I send a test email, it is allowed through and gets delivered.
Can someone please tell me what I've done wrong, and how to fix it.

Gary