Success!!! dunkenb had the right theroy,

4 bolts out.
move the seat unit back as far as possible.
lever the rear seat up and get the brightest torch you can find to shine in there.
Use another lever to force the seat unit back a little more and you can just see the lock mechanisum.
Then used a lever shaped screwdriver to release the seat.

I did try this at first but didnt have the balls to force the seat unit back far enough to see the lock.