Check fuses 7 and 8 in the fuse box by the battery (I think, check your handbook).
If they are ok it is probably the microswitch in the boot button or a corroded multiplug in the tailgate wiring loom.
What idiot thought "lets dump the simple, proven mechanical system which has worked for years and replace it with crappy electrics".
Oh yeah, the usual vauxhall idiot.
arfur888
May 2011