I have an 03 plate signum and had exactly the same problem. If you drop the seat and get into the boot there is a release catch in the middle of the boot panel, you can't miss it. just put a screw driver( i just used the car key) in the slot and turn. It even has arrows telling you which way to turn it. I've only had the problem since friday so am still looking for a solution as my boot release won't do anything. If you find a solution please let me know, dji8879 at hotmail.com,
thanks,
David
David Ireland, February 2010