Very simple, fast, and easy-to-use module that exports a subroutine that will confirm whether a year/month/day is a UK holiday.
The downside of the simplicity is that the holiday dates only run until 2007, and don't go very far into the past. More data is available on the DTI site referenced in the POD.
Also note, these are English holidays, not really UK holidays. I have updated the module to include dates up to 2010, and uploaded it as Date::Holidays::UK::EnglandAndWales.