all sorted, phew!
if anyone else is having this problem, the inertia reel wont work unless the seat is at the installed angle, so once the seat is out it will lock, if you pulled on the belt (like i did) then put the seat at the right angle, pop the 2 plastic clips off where it goes into the seat and use a screwdriver to roll the reel back a bit and this should release the latch and then you can pull the belt back out, easiest to do this when its back in the car.
anyone removing the seat in the future, pull the belt out a bit and tie a knot in it so you dont have this headache