Had the same thing happen to a 56 reg Audi A3, the fault was a corroded microswitch in the boot lid mechanism. I recently had to replace the boot lock mechanism on my Golf (different reason) and it took about an hour all in all, broken down - 10 minutes to replace the lock and 50 minutes to get the bloody trim back on!!!!!!!!!
Lock mechanism is about £40 from your local dealership - Part number 1K6 827 505