Yep, as andye has pointed out, I had the parameters the wrong way round.
In this use of LIKE, I'm simply using to to remove case-sensitivity, not for wildcard use.
It's usually faster and more obvious to do case-insensitivity by converting both to lowercase. You can use lc() in perl and lower() in most SQL databases. If you do this all the time and it performs badly, you might want to investigate building an index for the lowercased version of the column.