Hi there Richard.
To manually open your boot, you need to climb in from the rear seats. Once you get in to the luggage area you need to look for a small hole near to the latch. By inserting a screwdriver into the hole, you can then release the boot.
Apparently this is a common fault, and the release button will need to be replaced.
I did a google search, and it came up with a couple of videos on YouTube that show you how to do all that I have described.
Hope this helps, and you get it all sorted.
Regards Andy