One side of the catch has broken most probably.
Undo two nuts that hold the hinge in place just behinf the carpet at the back and unhook the hinge. Force the front of the glovebox down a bit so that you can undo the two screws that hold the front of the bracket that the catch engages with.
You should now be able to get a screwdriver in to release the unbroken side of the catch.
Alex wrote:once ive done this does it mean i need a new glove box
Not if you do it carefully. You'll just need a new catch.
Happened to me recently, in a fuel station forecourt, with an empty tank, and my wallet in the glovebox!
The first time it happened to me was blimmin miles from home, with the satnav in the glovebox, containing the directions to the hotel I was booked into! Anyone else?!
E30 in need of wiring loom smoke since April '11...